This movie is just awful, despite a decent cast. I love Adam Scott and Lizzie Caplan and the rest of them are alright - Kirsten Dunst, Rebel Wilson, Isla Fisher, James Marsden.
Rebel, Kirsten, Isla and Lizzie are friends from high school, but not really. They clearly don't like Rebel. Anyway, the 3 girls are bridesmaids for Rebel's wedding, Kirsten being the MOH. They reminisce about calling Rebel Pig Face in school and they comment that her FI is actually good looking.
Kirsten is a great bitchy MOH and gets things done for Rebel, but she can't stand that Rebel is getting married before her. She "does everything right" - went to college, eats well, exercises, has a boyfriend in med school - and still isn't engaged before Pig Face.
The other two are party girls, Isla being the air-head type, Lizzie being the sarcastic type.
The 3 bridesmaids are just awful people and much shenanigans ensue. The movie follows the 3 of them trying to get Rebel's wedding dress fixed after two of them got into the dress together for a FB picture to show how big the dress had to be for Rebel to wear it. It's ripped, bled on, used as a splooge towel, etc.
They end up getting it mostly fixed and to the wedding just minutes before it began. She wore it in the wedding and was completely clueless as to what had happened the night before. And then it ends, with Rebel thinking they are great friends and never finds out that they're just terrible.