Tommy Boy

Rob Lowe played the supporting role of Tommy's stepbrother and is uncredited. The reason for this is because he wanted to be a "happy surprise" after the script shifted focus (the film was originally centered around the relationship between Tommy and Paul). Rob was playing tennis with Lorne Michaels, and Lorne told him that he was about to start "Tommy Boy" and that he was considering him to play Chris Farley's brother. He ended up taking the part as a favor for Lorne, since he was previously in Wayne's World (1992).

During filming, David Spade and Chris Farley got into a physical altercation on set. As they landed in Toronto on an early Sunday morning after doing SNL in New York, Farley was not feeling well, so he went up to his hotel room. Spade, not thinking anything of it, had called up Rob Lowe and they went out to a bar for a drink. Farley found out the next morning and had become very jealous and throughout the morning would angrily stare at Spade and repeatedly ask him, "How's Rob Lowe?". Spade tried to explain and reminded him, "Word off the wire was that you were sick", but Farley wasn't trying to hear it. Later that day, they were about to shoot a scene. Spade was sitting on the ground eating a tuna sandwich and going over his lines, while Farley, smoking a cigarette, was still just staring and asking him "How's Rob Lowe?". Spade was getting annoyed with him at this point. Farley then went over to Spade and stomped on his hand with the sandwich in it. Spade responded by throwing his Diet Coke on him, to which Farley threw Spade into a wall and pushed him down a small set of steps. Before things got too violent, the walkie-talkie called "action", they quickly composed themselves and walked into set. Then, when it was time for Spade to say his line, he couldn't speak, so he stormed off set into his trailer. The director called cut and Farley went off to his trailer, too. Spade refused to continue filming with Farley. Farley was so mad that he needed to hit someone, so he tackled the director's assistant, Skippy (who was about the same weight/build as Farley). The pair would sometimes go for hours without talking to each other, they would talk to each other through the director.

On the list showing the exam grades of the students at the beginning of the movie, look at the bottom. One of the names is Helen Keller, who scored an F. Also look to the right of Helen Keller, you'll see Michael Jackson, he got a D+.

David Spade said the "fat guy in a little coat" routine began as an in-joke between him and Chris Farley when the two shared an office together working at Saturday Night Live (1975). Farley would often break up the monotony of their writing time by repeatedly pranking Spade with the idea. He would always insist that he had new material to show Spade, then turn around and reveal it to once again be the "fat guy in a little coat" joke. Spade said he and Farley decided to use it for this movie, thinking that if it was funny to them, it may be funny to others as well.

David Spade (Richard) and Chris Farley (Tommy) had to fly back and forth from Toronto to New York to rehearse and perform on Saturday Night Live. They were still cast members at the time.