Robert De Niro used anti-Semitic remarks to anger Jerry Lewis while filming the scene where Rupert Pupkin crashes Jerry Langford's country home. Lewis, who had never worked with method actors, was shocked and appalled, but delivered an extremely credible performance.
Much of the scene where Rupert shows up at Jerry's house was improvised. Kim Chan improvised his lines when Jonno calls Jerry. The part where Jonno has troubling opening the front door was not planned. Chan really could not open the door and Jerry Lewis improvised his reaction.
When Jerry Langford is walking down the street, he is stopped by a woman talking on the telephone. When Jerry refuses to talk to someone on the phone, the lady says I hope you get cancer. This incident actually happened to Jerry Lewis. According to Scorsese, Lewis directed this segment himself.
Martin Scorsese said later that making this film was an "unsettling" experience, in part because of the embarrassing, bitter material of the script. Scorsese said that he and Robert De Niro may have not worked together again for seven years because making The King of Comedy (1982) was so emotionally grueling.
Actor-comedian Jerry Lewis played a character, Jerry Langford, with the same first name as his own. Jerry Langford was originally named Bobby Langford in the script. But Lewis suggested that the character be named after him so that they could film reactions from real passersby who recognized him. None of the other people in that scene were actors except for the cabbie and the woman on the payphone.
Jerry Lewis found Martin Scorsese's working method initially frustrating, as he was made to wait around for the first 3 days of shooting. Lewis told Scorsese that he was a professional and was going to get paid for all the time he was made to wait, and that if Scorsese wasn't going to use him, then he could tell him that he wasn't needed.
When Rupert is talking to Rita in a restaurant, a man in the background is imitating Rupert's hand gestures. The man is played by the actor Chuck Low, who also appeared in De Niro and Scorsese's next collaboration Goodfellas (1990) as Morrie Kessler.
In his monologue on the Jerry Langford show, De Niro's character Rupert Pupkin says that he is from Clifton, New Jersey. This is possibly an allusion to Andy Kaufman's abusive comedian persona, Tony Clifton, whom Pupkin resembles with similar hair, mustache and cheap blue suits.
In the original script, when Rupert and Rita meet in the diner, there is a stranger sitting behind Rupert who flirts with Rita; later this stranger propositions her successfully. Although he is glimpsed in the film, it is not clear what he is doing. Another change is that in the script, when Rupert is being interviewed by the authorities who are looking for Jerry, Rupert is beaten, this does not happen in the film.
The talk show segments were filmed on videotape (like a real talk show) and later transferred to film. An unedited version of Jerry's monologue in its original video format can be seen as part of the DVD's special features.
Liza Minnelli filmed a scene where she played herself on Jerry Langford's talk show and sang "New York, New York" but it didn't make the final cut. Minnelli only appears in the finished film as a life-size cardboard cutout, a guest on Rupert Pupkin's basement talk show.
Man in van - as Jerry Langford is walking across the street and is greeted by a woman at a phone booth where she wants him to talk to her nephew Morris, Scorsese can be seen in the driver's side of a green van.