No effects or prosthetics were created for Stu's missing tooth. Actor Ed Helms never had an adult incisor grow, and his fake incisor was taken out for the parts of filming where Stu's tooth is missing.
Lindsay Lohan was offered the part of the stripper, Jade, but turned it down. She did not like the script and thought the movie would bomb. Heather Graham was given the role instead. Lohan later admitted to regretting the decision.
During filming in Las Vegas, one of the Mercedes (a very beat up and distinctive one) was stolen from the lot where the vehicles were being kept. The next day the production was filming driving sequences and traffic was being held up by the local police. A production person noticed that a very distinctive Mercedes was part of the cars being held, the police were told, the driver was arrested and the car was recovered.
According to Celena Haas (Caesars Palace Director of Public Relations), the suite the characters stayed at was modeled after two of the resort's luxurious suites in its Forum Tower: a well-appointed penthouse and the so-called "Rain Man (1988) suite," located on the 68th and 69th floors of the Forum Tower.
The song that plays during the scene in which Neeco the tuxedo deliveryman tosses the guys' rented tuxedos into their speeding car is "Ride the Sky II" by Revolution Mother. Neeco is played by Mike Vallely, Revolution Mother's lead singer.
[Chuck E. Cheese]
Alan makes a joke about him not being allowed near schools or a Chuck E. Cheese, a direct reference to one of his staple jokes in his stand up: "When you look like I do, it's hard to get a table for one at Chuck E. Cheese."
The trivia items below may give away important plot points.
According to Bradley Cooper, while giving a speech at a Toronto screening: "the people in Las Vegas never even noticed [a] movie was being filmed." He said that he had tiger scratches on his neck, all bloodied, and Justin Bartha was beet red, and nobody noticed, or even stopped to double-take.
Ken Jeong improvised the nudity in the scene where he jumps out naked from the trunk. Originally his character was meant to have clothes on, but Ken suggested that his character be naked instead. Later, director Todd Phillips gave Ken a nudity waiver slip to sign in case Ken changed his mind on the nude scene.
In the MPAA green-band trailer, Ken Jeong is wearing digitally-added underpants when he jumps out of the trunk, and Bradley Cooper says "paging Dr. Douchebag" to Ed Helms instead of "paging Dr. Faggot".
The escalator scene in the casino is a tribute to the movie Rain Man. Zach Galifianakis and Bradley Cooper have to win $80,000 in order to pay back Ken Jeong's character. This is also the amount needed to win by Dustin Hoffman and Tom Cruise in Rain Man.