When Christopher Walken and Rachel McAdams are dancing at the engagement party, Walken kept saying "fart" to keep McAdams smiling after dancing had become quite repetitive.
The painting given to Jeremy (Vince Vaughn) by Todd (Keir O'Donnell) was kept by Vaughn after filming.
Bradley Cooper was hired at his audition. As director David Dobkin recalls, "My saying is that you never, ever hire someone in the room; you always have to go back and watch the tape. Bradley Cooper is the only person who was an exception. I couldn't find anyone [for that role], and then he came in the room and he was amazing. He was like a thoroughbred. I remember going up to him and saying, 'Dude, you're awesome! You got the part!'"
Rachel McAdams got her certification in sailing to prepare for her role. She says she can now handle a 26--foot boat.
Following complaints from the United States Congress, the producers of the film yanked from the movie's official web site a printable Purple Heart advertised as a gimmick to pick up women and get free drinks.