John Beckwith (Owen Wilson) and his best mate Jeremy Grey (Vince Vaughn) are dedicated and professional wedding crashers who live each year for "wedding season" where they use the tried and tested set of rules as passed down by legendery crasher Chazz (Will Ferrell) to sleep with as many bridesmaids and guests as possible.
  The problem is that at the Secret Service protected Cleary wedding, John has broken the rules and fallen for Claire (Rachel McAdams) and needs his wing-man around - while Jeremy just wants out from his infatuated latest conquest Gloria (Isla Fisher)!

After Claire's boyfriend exposes their plan, with the help of a PI, and both John & Jeremy are asked to leave the Cleary mansion - Jeremy finally realises that he is just as messed up as Gloria and declares his love to her on the way out.
  Later, John tries to crash Claire's engagement party dressed as a waiter, but is beaten up by 'Sack' Bradley and his friends - and learns that this Bradley is not the greatest fiance in the world. On his way back to Jeremy's, he finds out that Jeremy and Gloria have been together all this time without telling him.
  John is despondent and a wreck, he won't return Jeremy's calls, or show up for work, and reads self help books such as "Don't Jump".  He crashes weddings on his own without any success, usually getting wasted at most of them. When Jeremy finally calls round they clear the air - until Jeremy reveals he is about to get married - and he wants John to be the best man. John kindly asks him to leave.

John seeks out Chazz, who tells him about the next level - funerals! They go to a funeral together, and sure enough Chazz is onto a winner ... but John just doesn't feel right.
  He makes his way to the wedding of Jeremy and Gloria and disrupts the service. He is allowed up to the front as the rightful Best Man, but as he tries to talk to Claire she can't take it and walks away down the aisle.  Unlike in real life, everyone in the church is quiet and gives John time to deliver a long, heartfelt speech. Bradley then reveals his true self when he shouts at Claire. As he runs to hit John again, Jeremy steps in and smacks him down.
  John and Claire kiss, and everyone seems happy enough.

They leave the church together - Jeremy & Gloria (married) with John & Claire, and plan a roadtrip to crash the nearest wedding party they can!