NOTE: This spoiler was submitted by Joanna
Regan (Kirsten Dunst) and Becky (Rebel Wilson) are out to eat. Regan is ordering healthy food and Becky, who is overweight, is ordering fatty food. She tells Regan that she is engaged to her boyfriend Dale (Hayes MacArthur).
Regan calls her friends, Gena (Lizzy Caplan) and Katie (Isla Fisher) and tells them, very upset, as she wanted to be the first one to get married, especially before her “fat friend.” She complains that now they will have to be in the wedding.
The Day Before the Wedding:
Katie is very excited to be in the wedding. She can’t wait for all her friends, the “b-friends” to be together again. She works at a clothing boutique and isn’t very nice to the customers. Gena sleeps around a lot and on the plane she is talking to the guy next to her about blow jobs and sex, and what would warrant giving a “10”. She reveals that her ex-boyfriend who ruined her life is going to be there, and she’ll see this guy again, so she won’t give him a blow job. At the same time, Regan is shallow and nasty to all the wedding planners.
The three friends are reunited at the hotel, wondering how they will get through the next 12 hours for the bachelorette party. Becky shows up thrilled to see her other two friends. The bachelorette party is impromptu, and all Becky wants to do is eat ice cream and drink champagne in the room after the rehearsal dinner, despite them wanting to have a huge party Gena and Katie run off to do cocaine.
At the dinner, Katie tells Gena she got a stripper for them that night. We are introduced to Trevor (James Marsden) who is the best man, and Gena sees her ex-boyfriend Clyde (Adam Scott). Joe (Kyle Bornheimer) comes over to talk to Katie. They went to high school together, and he seems to be rich now, but she doesn’t remember him until he tells her that he sold her pot.
Trevor is telling an embarrassing story for his toast, (Which wasn’t supposed to be until the next day) and Regan steps in with a surprise for Becky which are two women doing a rap for her. Gena stands up to give her toast, revealing that they met in their high school bathroom, and Becky was forcing herself to throw up. Katie steps in, and since they are both high it doesn’t turn out well.
Later on in the hotel suite a stripper shows up for all the women. Becky is into it until she hears him call her Pigface, which was her mean nickname in high school. Gena acts like it’s funny and Becky flips out on her, telling her and Katie not to bother coming to the wedding unless they are normal and sober before leaving.
Regan, Gena, and Katie are left in the hotel room drinking and snorting coke. Regan can’t get over the fact that Becky is getting married before her, and she’s miserable. Katie tries on Becky’s wedding dress which is too big for them. She and Regan both get in the dress and Gena goes to take their picture, and the dress completely rips. They freak out and bring the dress down to the tailor of the hotel, but they can’t do anything. Meanwhile, Regan is on the phone with her boyfriend Frank who can no longer attend the wedding due to being in med school and being busy that day. They discover that Katie’s nose is bleeding from the coke, and it got on the dress. In the hallway of the hotel, they run into Dale and his groomsmen, and he is blindfolded on his way to a strip club. They part ways but not before Gena pretends to come on to Clyde, stealing his wallet to try and help pay for the dress to get fixed.
The men are in a limo on their way to the strip club talking about finding the “right girl.” Meanwhile, the women are standing outside the bridal shop waiting for the store owner Melissa to show up, vowing they will never do coke again. Melissa shows up and hates them, especially Regan, and they tell her that Becky decided she wants a new dress. Melissa brings one down, but it’s a size too small. Regan flips out and refuses to buy the dress because it’s “her perfect dress.” She says she’d rather lick the sidewalk than have Becky wear it, and then she actually does lick the sidewalk. During this, they discover that Katie knows how to sew!
They go to a convenience store and Katie and Gena continue snorting and drinking. It’s 2 am, and they buy thread and now need to find a sewing machine. Meanwhile, Trevor keeps texting Regan to go to the strip club. At the strip club, Dale is very upset that they are going to show up and says he will wait in the car. The three ladies show up and aren’t allowed in the strip club without a male escort. They see Dale leaving, and he gets them in saying “they’ll fit right in.” They find the dress in the garbage bag outside the strip club and go inside to clean off the dress. Gena sees Clyde with a stripper and is upset, and Joe seems to be in love with Katie, who is dancing with a stripper on the stage. Trevor asks Regan to help Joe hook up with Katie, and they wind up in a history/political discussion. Clyde is trying to hook up with the stripper and realizes that his wallet is missing.
As Gena tries to clean the dress in the bathroom, she starts talking to a stripper who uses the dress as a towel and toilet paper without her noticing. Katie has gotten high on pot and Regan yells at Gena who is trying to confess to Becky over the phone. They all start arguing, and Regan yells at Gena saying she handles everything, including her abortion. This ridiculously upsets Katie since she wasn’t invited to go. Gena gets Clyde, and they leave together with the dress. Trevor gets Joe to take Katie home (and she drunkenly kisses him a lot) and tells him to “slip it in” (which he doesn’t want to do). He gives him some xanax to calm him down so he will be able to have sex with Katie without feeling bad.
Gena and Clyde argue on the subway since she stole his wallet and she is still mad about whatever happened between them which is the abortion. He was a few years older than her, and the issue was that he didn’t show up for the abortion, and she had to do it alone. Right now she just wants him to help her fix the dress. Meanwhile, Trevor and Regan are off talking at a lounge somewhere talking about puberty and girls hating themselves when they turn 12. They wind up having sex in the bathroom. Becky calls her in the middle of it, and she says she’ll be there in a few minutes.
Clyde and Gena go to his mother’s house. She obviously doesn’t like her but agrees to work on the dress. They have their little “moments” in the kitchen, and he keeps asking her who she’s calling, which is her friend’s cocaine dealer. He takes her phone and throws it outside telling her it’s not cute anymore. They wind up looking at old photo albums, saying that they were great together because they were friends. He tells her that he couldn’t show up that day because he was too sad. They go into his bedroom, and he starts showing her old things from his closet, and plays her a mixtape he made when they were in high school. He calls her Genny repeatedly, which she tells him not to call her, and they wind up having sex.
Joe and Katie go off on their own and go swimming in an indoor pool at the hotel. They share stories about being high and drunk, and she also tells him that she slit her wrist a year ago. He kisses her, and they get out of the pool. They’re going to have sex, and he asks her if he can do it another night instead because they’re drunk. He tells her that he likes her a lot and cares how they have sex and doesn’t want a random hook up with her. She can’t even remember his name. He leaves, both of them upset.
Regan goes to Becky’s room. Becky is very upset and tells her that she feels bad about what happened earlier, and she overreacted. She knows that Regan is having a hard time dealing with everything, and she wishes the stripper stayed. She thanks her for everything she’s done and Regan sneaks off to the bathroom and leaves another message for Gena on her phone. Becky opens the door and catches her about to throw up. They reminisce about high school a little bit and how Becky took the fall for Regan in high school saying that she was the bulimic one when in reality it was Regan. Regan is about to tell Becky about the dress when Becky’s mother shows up and tells them that it’s time for her to start getting ready since it’s morning.
Gena and Clyde wake up. She grabs the dress and runs out. Regan is flipping out, and the party planners say they can’t find the dress. She starts to change, and Joe walks in saying that Katie locked herself in the bathroom and won’t come out. Gena has the fixed dress and brings it back to the tailor in the hotel saying it’s fixed and asks her to clean it. She finally calls back Regan and tells her the dress needs 40 minutes. Regan flips out again on the party planner people because they got the wrong flowers for Becky. Regan finds Katie in the bathroom, and she seems to have OD’d. She tells Joe that she does this every weekend, and he tries to revive her. Meanwhile, Gena is pleading with the tailor to hurry up with the dress and to stay until it’s done.
Joe realizes that Katie took the xanax and calls the paramedics. Regan sticks her fingers down Katie’s throat and has her throw up the pills. She has a vomit stain on her dress now, and Becky and her mother are flipping out wondering where the wedding dress is. Gena knocks on Trevor’s door and hits him with a coffeepot for giving Joe the xanax. She then runs after them with the dress but misses them. She uses the same cab as Clyde who feels the need to tell her that they are meant to be together. Becky thinks her dress is being steamed and is flipping out thinking she’s going to get married in her pajamas. She’s screaming at her mother and Regan in the taxi saying she hates both of them. They get to the place, and Becky is screaming at Regan. Gena shows up with the dress and Becky notices the blood stain, flipping out, so they have to give her the brief rundown of what happened. She gets over it and walks down the aisle, leaving Gena and Regan, who has vomit on her, behind. Katie gets there late and the three of them sit on a bench watching the ceremony. At the reception Joe and Katie talk and kiss, Regan tries to sleep, and Clyde gives an obscene speech about having sex with Gena the night before which makes everyone laugh. He says he wants to do that forever and starts to sing “A Thousand Miles” to her before going to her and they kiss. Joe and Katie also dance while Regan tells Trevor to meet her in the bathroom on the dance floor. The four girls dance together as the film closes.