Rob Lowe played the supporting role of Tommy's stepbrother and is uncredited. The reason for this is because Rob was contractually obligated to Stephen King's The Stand (1994) at the time, so he took the part simply as a favor for friend Chris Farley.
According to David Spade, he and Chris Farley got into a physical altercation on the set. Spade had gone out for a drink with Rob Lowe the night before. Farley had become very jealous and angrily repeated "How's Rob Lowe?". David got so fed up with Chris hounding him on the subject that he threw his Diet Coke on him, to which Chris responded by throwing David into a wall and down the stairs. After the fight, Spade walked off the set and refused to continue filming. The pair would sometimes go for hours without talking to each other, talk to each other through the director, etc.
Peter Segal told Film School Rejects that at one point during production, scheduling conflicts almost forced Rob Lowe to drop out of the film. This resulted in the filmmakers holding impromptu auditions while the movie was already filming for the part of Paul Barish. Matthew McConaughey was one of the actors who auditioned. Eventually, Lowe's scheduling conflicts were resolved and he was able to appear.
According to David Spade, both he and Chris Farley ended up dating Lorri Bagley who played the naked woman at the pool. According to Spade, this caused some tension between them during the filming of Black Sheep (1996).
David Spade's character Richard Hayden says that 'Big' Tom, played by Brian Dennehy was like a father to him. Brian Dennehy would go on to play David Spade's father as Red Finch in the TV comedy Just Shoot Me! (1997)
Original working title was Billy the Third: A Midwestern . However Lorne Michaels was also working on Billy Madison and insisted the change. Other names considered included Fat Chance and XL before settling on Tommy Boy.
David Spade (Richard) and Chris Farley (Tommy) had to fly back and forth from Toronto to New York to also rehearse and perform on Saturday Night Live in which they where regular cast members at the time
When Richard walks into the mini-mart at the gas station to ask the man behind the counter for directions you can hear Patsy Cline's "Crazy" playing in the background. Julie Warner who plays Tommy's girlfriend Michelle in this movie was also the love interest of Michael J. Fox in Doc Hollywood (1991), in which "Crazy" was the main love theme that Fox and Warner's characters dance and fell in love to.