While filming the scene in the bar where Carl runs into a waitress and falls on his back, Jim Carrey did the stunt incorrectly, fell to the floor harder than he expected, and broke three ribs in the process.
Jim Carrey's bungee jump stunt was the final scene filmed, but not before it caused many problems for the insurance company and the producers, due to his insistence of performing the stunt himself. The insurance company was not willing to underwrite a premium for a lead actor over a stunt double. Finally, an agreement was reached between both parties, with the producers assuring two things to the company: the stunt to be performed after filming technically ended; and the scene could only be filmed once. Eight cameras were used to film the stunt, and Carrey performed it uninjured.
Just like his character, Jim Carrey said "yes" to many things during the production of this movie. He indeed truly played the guitar, learned basic Korean, rode a sport bike and bungee-jumped. He however had to say "no" for the body blading scene.
The day before Zooey Deschanel had to get on the scooter for the first time, her stunt double fell off and shattered her hip. Zooey was told that it would take the stuntwoman about nine months to recover, so she was asked to get on the bike for the shot.
Jim Carrey was seduced by the project, as he felt it would enable him to act in some truly funny scenes which would also make the audience think about themselves and wonder if they should perhaps say "yes" more often.
After Carl's (Jim Carrey's) big bender and fight at the club, there is an overhead pan of Carl lying on a bathroom floor. The clothes he is wearing, the positioning of his legs, arms, and head and the scratching guitar music score is an homage to David Bowie's album "Lodger", and its cover photo.
Carl makes two references to The Beatles in this movie. The first is when he sings "Can't Buy Me Love" in the Hollywood Bowl, where The Beatles frequently played during Beatlemania, and the second one is when he plays the guitar, singing "Jumper" by Third Eye Blind, and shouts after finishing, "I've got blisters on my fingers!" This refers to the song "Helter Skelter", in which Ringo Starr shouts this after the song ends.
Director Peyton Reed spent a lot of time with Jim Carrey to find the right tone for the film, one which would be in between Carrey's manic comedies and his more serious-minded films, as well as to complete the subject's Americanization, as the source book comes from a British author.
The fictional band "Munchausen By Proxy" featured in the film is named after the Münchausen syndrome by proxy, which is a psychological disorder, and is composed of Zooey Deschanel and the real-life band "Von Iva", which got the part after Music Supervisor Jonathan Karp saw the cover of their CD in Amoeba, in Hollywood. On Lakeshore Records' soundtrack release, they are credited as "Munchausen by Proxy (f/ Zooey Deschanel & Von Iva)".
The scene where Carl is sitting down watching The Ghost and Mr. Chicken (1966), is a tribute to the late Don Knotts. Jim Carrey was slated at the time to star, and approved by Don, in a remake of The Incredible Mr. Limpet (1964), but Knotts passed away shortly before filming began on this movie, and Jim felt that it wouldn't feel right to accept the role.
There is a scene where we see Carl (Jim Carrey) watching Saw (2004) in his apartment. The scene he is watching contains Cary Elwes. Jim Carrey starred in Liar Liar (1997), which also starred Cary Elwes.
When Norman (Rhys Darby) is trying to be friendly, he tells Carl (Jim Carrey) to take this "to the next level". He also calls him "broseph", and remarks that it's a combination of "bro" and "Joseph". This is a reference made to a popular YouTube video by Balloon Shop titled "Take It To The Next Level" where the protagonists say "yeah" and "yes" twenty-three times.