The movie begins with a view of a house at night (the last night of Summer break). Wade and Ryan talk on the phone. Both are excited about their first day of high school. Ryan tells Wade he can get a girlfriend as long as he doesn't come off needy. Ryan also wants to go by "T-Dog", since it sounds cool. Wade wants a nickname, to which Ryan replies that he already has one (Skeletor -- due to his thin frame). Wade busts Ryan's chops over his weight and the two quarrel for a bit. Wade's step dad then barges in and yells at him for being on the phone at 3 am. He hangs up Wade's phone and before leaving, criticizes Wade for having such a nerdy room.
The next morning we see each of the three characters' morning routine. Drillbit Taylor (Owen Wilson) wakes up and climbs out of his makeshift tent to the title credits. Wade is awoken with a football spike by his two stepbrothers. Ryan is awoken by his mother, who pulls off the sheets only to realize he's started sleeping naked. The two freak out for a second, with his mom asking when he started this. Ryan remarks that he doesn't want the elastic squeezing his ass when he sleeps. Wade showers and has fantasy conversations with girls. Ryan raps in his shower. Drillbit showers out in public using the beach's public rinsing shower. Wade has breakfast with his family, with his stepbrothers teasing him about his hobby (magic). Ryan yells at his mom for forgetting the sausages at breakfast. Drillbit walks in bumper to bumper traffic asking for money. One man gives him money, but writes on the bill "not for pot", thinking that will stop anything. Wade's step dad tries to convince him to lift weights with him and the boys. Wade passes and calls them freaks. Ryan finishes a phone call from his dad (the two parents being divorced). Afterwards, he assures his mom that he thinks "he's a piece of shit". Drillbit sees one of his "regulars" (played by Lisa Lampanelli), who jokes that he should spend the money on porn only.
Wade waits at the bus stop. Ryan walks up and the two are mortified to see they have the same shirt on. They realize one of them has to change, and since Ryan can only finish the mile in 21 minutes, Wade will have to be the one to rush home and change. However, before he can get anywhere, the bus arrives so the two are stuck wearing the same shirt. The bus driver remarks, "Let me guess: Two for one sale at Hot Topic"? The two arrive and find their lockers are across from each other. Wade has a little problem working his locker, and is helped by a girl, to Wade's delight. Afterwards Wade and Ryan look on as a nerd named Emmit is helplessly stuffed in a locker by two bullies named Filkins and Ronnie. Wade decides to speak up and tell them to stop. The two bullies make Wade their new target as the nerd escapes. When the bullies see that Wade and Ryan have the same shirt, they stuff Wade's arms into Ryan shirt to keep them stuck together. The also threaten them to stay that way or they're dead. The two comply and walk into class to the sounds of laughter. The teacher, named Lisa (Leslie Mann) remarks they look like "those Velcro monkeys that hug each other".
The next scene is of Wade at the dinner table, where his mom asks how his first day was. Wade lies and says it was great. He says he made so many friends he can't remember all their names. He high fives his family before humorously sobbing while he drinks his milk. Ryan also lies to his mom, saying it couldn't have gone better. His mom says they were probably impressed by his shirt. Meanwhile, Drillbit tries to stop two officers from taking down his tent. They inform him his stuff is in the dumpster. Drillbit argues his taxes pay their salary, only to be reminded he doesn't pay taxes.
Wade and Ryan get off the school bus on their second day, determined to make a fresh start. Wade sees Brooke (the girl who helped him with his locker the other day). Rather than making a move, he just signs up for the same clubs as her (Photography and Asian Heritage). Wade and Ryan are then met by Emmit who happens to be wearing the same shirt they had on yesterday. He introduces himself and thanks them for their help the other day. Ryan warns Wade that associating with him will hurt their cause. The three run into Filkins and Ronnie who let the three know that they'll be riding them forever. We next see a montage of humiliation. One day, at the urinals, Filkins and Ronnie ambush the three and cause them to urinate on each other. The next day, we see Emmit's laptop ruined when a drink is poured on it. The very next day, we see Wade trapped in the school's trophy case. Ryan's locker is broken into and filled with pictures of half naked men. The next day, all three have their pants pulled down. Other examples are Wade's disposable camera broken, Emmit attacked at the bathroom yet again, Wade and Ryan shoved against their lockers, Emmit hanging from his book bag's strap, and Ryan launched down the hall in a swivel chair.
Meanwhile, Drillbit is hanging out with some of his homeless friends, including a man named Don. Drillbit is frustrated by his life (after losing the lottery yet again). He remarks how the rich hate them and the tourists are scared off by them. He claims Canada (where he wants to go) will pay you to take their most northern land, the beer is twice as strong and that British Columbian girls have the sound of an ethnically potent mix. He figures if he can raise a few hundred dollars he can be on his way.
Back at Ryan's, the two watch TV while Emmit does a spastic dance. Ryan doesn't want him around, but Wade seems more accepting. Wade says he has an idea about their bully problem. He claims that on the internet there are people advertising themselves as bodyguards. Ryan is hesitant about the idea. The next day at school, the three try to talk to Principal Doppler (played by Stephen Root). Doppler gives Filkins the chance to defend himself. He apologizes and comes off very polite. He claims he was just doing a little hazing but meant no harm. We also find out that Filkins is emancipated, so he really doesn't have to answer to anyone. After school, the two bullies chase the three with their car. The three cut through a lawn with two girls sunbathing, but not before posing for a couple of pictures. They eventually duck into a closing garage door just in time. Ronnie and Filkins bang on the door yelling threats. An old man yells inside the garage at Wade, Ryan and Emmit to get off his property. On the other side, Filkins and Ronnie think the man is yelling at them, threatening to get his shotgun. The garage door is opened again, and we see the coast is clear. That night, Wade posts a help wanted for a bodyguard. Meanwhile, Drillbit uses someone else's computer.
The next day, the three interview candidates. The first is of a black hip/hop bodyguard (though he actually likes country music) asking for $2,100/week. The second is a former Mossad agent ($10,000/week). One man is a sketchy looking man covered with tattoos. The next is a man who claims their needs are ridiculous. Another is a man who is way into tigers, and another is Chuck Liddell. One man (played by Frank Whaley) tries to prove himself, only to get laid out by an average man. Everyone is out of their range, so their search seems to fail until they meet Drillbit. He claims to have a lot of military and weapons expertise. He claims to have protected three vice presidents, Bobby Brown, and Sylvester Stallone. He gives his price ($387/week). The three conference and say that at the moment they can do $83/week. Drillbit asks for the money in advance, and then makes a wing out of his arm, saying they are now under it. They walk to Wade's, where Drillbit says he will infiltrate the school so well they might not even see him around. He starts picking expensive items and dishes, saying they will come in handy as protection, surveillance, etc. Wade's mom comes home, so Drillbit sneaks out.
Drillbit heads to the pawn shop to sell the merchandise. He tells his friend that he'll take the cash value as well as the $83 to make his way to Canada. His friend tells him that he should keep milking money out of the kids before he makes his way. The pawn shop owner and Drillbit haggle on the price, when a walkie talkie he took goes off. Wade and Drillbit talk, and Wade lets him know they have more money (Emmit has Bar Mitzvahs money). Drillbit changes his mind and stays in town.
The next day, Wade repeats that today will be a fresh start. Ryan hopes so saying nothing good came from last week. Emmit remarks last week they became friends, to which Ryan repeats that nothing good came out of last week. Drillbit meets the kids outside their school. Ryan shows them where the bullies are hanging out and wants to see Drillbit beat them up. Drillbit tells them it doesn't work that way. He says that instead he'll train them to be able to beat them up. After school in the woods, Drillbit asks Ryan to charge him. He does and Drillbit barely manages to get him down. He claims to have taken him down with a Bear Hug. He does the same for Wade and Emmit and manages to shove them away, making himself look like a big man. Ryan falls down and finds Drillbit's tent. He explains it is a strategic outpost. In a training montage, he scares Emmit straight into a tree and then blocks a large branch swung by Wade (though he hides his pain from them).
Back at Ryan's, the two watch a movie and it gives Drillbit an idea that as long as people "hold one of them back from acting crazy", they'll look tough enough not to fight. Drillbit then hangs out with Don. He complains that even though he's not getting that much money, he enjoys the kids company ("The fat one says some funny shit"). However, the two rationalize an idea of robbing them by saying it will give them character ("Steal their TV. They'll read a book"). Back in the woods (their training area), Drillbit reminds them when they go back to school, they'll still be under his wing. He also tries to cop out of his training by saying that the most unexpected thing they can do is "love their enemy".
Wade sees Ronnie and Filkins rapping in the schoolyard. He tells Ryan that since he loves rap, he should go over there and find commonality. Ryan tries, but it turns into a rap battle with hostile words. Ryan gets the better of Filkins, and nervously runs off afterwards. Ronnie and Filkins track them down and claim they are going to get it even worse now. Wade uses Drillbit's idea and has Ryan hold him back. It backfires since it just gives Filkins an open target and punches him in the face. As the three walk home, Ryan complains that Drillbit wasn't there when they needed him. Drillbit waits along the street and sees Wade's face. He feels bad, but says that maybe they didn't use his advice exactly the way he intended. Ryan doesn't buy it and wants him fired. Drillbit yells that they've only gone through phase one. He says he plans to start phase two by going in with them to school the next day.
Back at Wade's, his step dad is in his massage chair. He sees Wade's black eye and has a chat with him. He says that bullies can be helpful (he was a bully in his past) in helping the weak get ready for the harsh world. The next day, Drillbit goes into the school posing as a substitute teacher. At the teacher's lounge he meets Lisa (the English teacher). The two seems to hit it off (he calls himself Dr. Illbit) and flirt on the couch. It gets heated after the 5 minute warning bell goes off, with Lisa saying Drillbit could probably get a lot accomplished in 5 minutes. Meanwhile the boys are watching a video at sex ed about the clap. In the hallway, Wade is delighted to see Brooke walking in his direction, but is terrified to see Filkins isn't far behind. Drillbit stays loyal and suggests the two meet up during 6th period. He takes off trying to find the kids. He can't make it through the crowd in time, so he takes a student's model castle, lights it on fire and hold it up to the sprinklers. The school gets evacuated.
During a class that Drillbit subs for, he protects Emmit by forcing Filkins to read romantic poetry (with homo erotic tones) in front of the class. Anytime Drillbit is called in to sub for a class with the two bullies, he gives them a harder time than the rest. Meanwhile, word is spreading how Ryan beat Filkins in a rap battle. Throughout the day, Drillbit follows Filkins & Ronnie and communicates their movements to Wade through walkie talkie. He also lets him know what Brooke is up to.
Outside of school, Drillbit meets up with his friends and says that as long as he has a coffeecup, none of the other teachers ask questions. This gives his friends the idea to try it themselves. At "Dr. Illbit's birthday party" held at the lounge, Lisa passes him a note, asking to meet after school. We then see a montage of the two meeting for sex everyday during 6th period. Drillbit starts to have feelings for her and works up the nerve to ask her on a real date, to which she says yes. At the Asian Heritage club, Brooke asks what Wade is doing there. Wade claims to be part Asian, but eventually admits that he's been joining her clubs to get a chance to talk with her. She reacts that he can't quit now, and that she'll make him come to all the meetings, which seems to please Wade. At home, Wade seems more confident, even though his parents suspect drug use (since he's always out of money).
Wade meets up with Drillbit at his "strategic post" and tells him about Brooke. Drillbit encourages him, even talking in mismatched slogans ("It's like the army says: Have it your way"). Wade gives him a gift: A framed picture of the four. Wade takes off, and we can see that the gesture has touched Drillbit. At his date with Lisa, the two has wine by a campfire. Lisa admits that in her past, she's been with such low-lives. This causes Drillbit to back off from confessing who he is.
One morning, while Drillbit is showering in public again, Ronnie sees him out of the passenger side. Driving the car, is his mom--who just happens to be Drillbit's "regular" from earlier in the movie. She tell Ronnie he must be mistaken, but Ronnie is convinced and now knows Drillbit's secret. Drillbit meets with his friends before school and lets them know the plan to rob Wade is off. Don argues with him saying "you can't polish a turd". Ronnie meets up with Filkins and tells him what he knows. The two ambush the three, and Drillbit rushes down (he was on the second floor of the school) to try and save them. Ronnie and Filkins aren't threatened anymore by Drillbit and call him a bum, confusing the kids. Filkins punches Drillbit, and the three kids run away.
Drillbit catches up and tries to explain that he's not a bum and just took a shot for them (like a secret service agent) and that he can't beat them up in front of the school. The kids seem to buy it and go to Wade's. However, when they walk in, they see Drillbit's friends in the process of robbing the place. A lot of confusion ensues since they see Drillbit knows them. Drillbit tries to stop them, but just gets punches again, this time by Don. They run off, and Wade yells at Drillbit, now sure that he's a fraud.
Drillbit comes clean (his real name, Bob) and tells them he served half a day in the middle east before sneaking on a cargo plane and going AWOL. With his facade broken, the kids kick him out. Drillbit then calls Lisa and comes clean to her. At his tent one night, the boys call through the walkie talkie, telling him they are going to call the cops on him. Meanwhile, Don gets out of a van (filled with Wade's stuff) and talks to a man about a good price. He then gets ready to back up the van to unload, only to see Drillbit at the wheel. Don taunts him, knowing Drillbit isn't capable to a real fight. Drillbit replies by kicking him in the face and takes off in the van. Wade gets ready to show his family their empty living room, only to turn the lights on to all their stuff piled up in the center of the room. Emmit says Drillbit must have brought it back. Wade's step dad makes him come clean. The next scene is of all the parents at the principal's office with the kids and Filkins. The principal says they have video of Drillbit and the cops will be looking for him. Ryan says that they did all this because of Filkins. Principal Doppler asks Filkins if this is true, but Filkins just manages to charm his way into everyone believing him again.
At a convenience store, Drillbit finally wins with a lottery ticket (winning $500). He makes plans to finally head to Canada. Meanwhile, Wade prepares to ask Brooke out. The two sit at a table, but are interrupted when Filkins sets off two exploding soda cans. He slaps Wade around and calls Brooke a "ho", before walking off. Wade, sick of it all, catches up with him and challenges him to a fight, anywhere he wants. Filkins chooses his house, where he could do anything he wants. Afterwards, Ryan asks what they should do next. Wade says they have to learn how to fight.
Not knowing what else to do, the two play video games, eat Powerbars, watch Fight Club, and practice taking punches from each other. The two write their goodbye letters to the world and drink a Red Bull before the fight. They arrive at the party/fight wearing the matching shirts from earlier in the movie. Meanwhile, Drillbit sneaks back into Wade's to return a serving plate he took from their first meeting, only to see the note Wade left behind for his family. At the party, Ryan (who wants no regrets) kisses a random girl, only to get slapped. The two meet Filkins and he's surprised they even came. He taunts them a little before Wade kicks him in the crotch and Ryan punches him across the face. The two celebrate their victory, only to come to the realization that he's getting up and the fight is long from over. The three fight for a while, with the 2-1 handicap playing only a small advantage. However, Ronnie shows up, and they force Wade and Ryan outside.
Out of nowhere, Emmit jumps on Filkins leg and manages to take him down. Ronnie comes in and knocks him out with a punch. Ryan retaliates by giving Ronnie a crippling Bear Hug. Wade trades punches with Filkins. Ronnie lies and says he can't breathe, causing Ryan to let go. Ronnie then punches Ryan and holds Wade from behind. Before Filkins can do much damage though, Drillbit comes to the rescue. At first he simply tries to stop the fight, but Filkins just punches him. Ryan tells him to kick his ass, but Drillbit says he can't since he's a minor. They correct him, and let him know he's 18. This changes everything and Drillbit unleashes a few moves before knocking him out cold. Ronnie backs away, swearing that he's only 17. Filkins runs back inside while the cops start to arrive.
Drillbit is about to take off (because of the cops) when Filkins comes running out of his house with a samurai sword. He throws it at the kids, only for Drillbit to catch it with his bare hand. We see something drop off his hand (his pinky finger). Unfortunately, one of the cop cars run it over with their tire. The cops tackle Filkins and take him and Drillbit in (of course Drillbit first heads to the hospital). Some of the guests at the party congratulate the three on standing up to Filkins. The cops question a scared Ronnie, while Wade talks to Brooke, and the two eventually share a kiss. We also see that the whole ordeal has bonded Ryan and Emmit.
In the epilogue, we see Drillbit writing a letter from jail. The boys have been sending him Captain Crunch (his favorite cereal). Filkins was sent back to his parents living on Hong Kong (who don't seem to be very happy with him). We see a shot of the kids goofing off and finally having a good time in school. Drillbit doesn't get his pinky back, but doesn't seem to mind that much. He says it reminds him of their battles together. He says that he should get out fairly soon due to work release and that he has been in contact with Lisa.
Flash forward to Don in handcuffs, being brought to jail for who knows what, while Drillbit is finally released. He is greeted by none other than Lisa, Wade, Ryan, and Emmit.
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