Martin Scorsese has said that he thought Robert De Niro's best performance under his direction was in this film.
Much of the scene where Rupert (Robert De Niro) shows up at Jerry's house was improvised. Kim Chan improvised his lines when Jonno calls Jerry. The part where Jonno has trouble opening the front door was not planned. Chan really could not open the door, and Jerry Lewis improvised his reaction.
In the scene where Robert De Niro and Sandra Bernhard argue in the street, three of the "street scum" that mock Bernhard are Mick Jones, Joe Strummer, and Paul Simonon, members of the British punk rock band The Clash.
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.
Jerry Lewis played a character 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 or actresses except for the cabbie, and the woman on the payphone.
Cathy Scorsese: The daughter of Martin Scorsese as Dolores, a fictional fan of Rupert who appears in one of his daydreams.