Jane Seymour was called in three times to audition for the role of Kathleen Cleary. Reportedly she beat out many, many actresses in their fifties and early sixties, also auditioning for the role of Mrs. Cleary.
When Jeremy first pitches to John the idea of crashing Cleary wedding, he hands him a section of a newspaper that carries the wedding announcement. It bears a photo of the bride and groom and a photo of Secretary Cleary accompanied by multi-column article. Though the announcement begins conventionally enough, by the point in the article that appears to the left of Christopher Walken's photo, the text reads: "The Cleary's are the center of the political scene these days with the potential candidacy of William for the president of the United States.
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.
The schooner Woodwind featured in the movie is an actual schooner available for charter and public cruises out of Annapolis, Maryland. In fact, they used the boat "as-is" including keeping her name unaltered. The boat featured is the second Woodwind (Woodwind II) and has an identical sister that bears the name "Woodwind". An employee of the Woodwind tours was actually laying underneath Walken steering the boat down the Severn River in Annapolis, while he is holding onto the wheel.
When confessing to the priest, Jeremy mentions that he had an imaginary friend named "Shiloh". This is apparently a reference to the Neil Diamond song "Shiloh", also about an imaginary friend.
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.
At the beginning of the film, when John and Jeremy are going over their plan to get into Christina Cleary' wedding, one of the senators is 2008 Republican presidential nominee John McCain. The man next to McCain in that scene (who gets a hug from Rachel McAdams' character) is Democratic strategist James Carville.
When Jeremy tells John, "You've crashed a million weddings, and you rocked them all", it is a reference to the Jon Bon Jovi song, "Wanted Dead or Alive". The song contains the similar lyric, "I've seen a million faces, and I've rocked them all."
The script was based on The Partygoers, San Francisco's premier party-visiting visionaries. Formed in 1997, the Partygoers are dedicated to spreading goodwill through the spontaneous visitation of social gatherings and celebrations.
This movie features a married couple portrayed by a former James Bond Girl and a former James Bond Villain, from different movies. Jane Seymour played Solitaire, the Bond Girl in Live and Let Die, Roger Moore's first outing as Bond. Christopher Walken played Max Zorin, the Bond Villain in A View to a Kill, Moore's last outing as Bond.
The Cleary home is actually a property called Ellenborough, on Peachblossom Creek in Easton, MD. Now owned by David Bradley, the Chairman of Atlantic Media, Ellenborough dates back to 1659, with the 2012 house dating back to 1928. It was once owned by a member of the DuPont family.
John and Jeremy's characters were loosely based on the great Wedding Crashers from northern New England, J.C. Cunningham and D.J. duBois. The two men own a maple syrup conglomerate in Vermont and spend their free time destroying commies, and lighting up the pigskin.