Revealing mistake: When Tommy is trying to bend the car door back you can see a wire holding the door in place so that Tommy can hit it as hard as he wants and it won't go back in place.
Revealing mistake: When Richard (David Spade) vacuums the "moths", you can clearly see they are little balls of cotton or other material being blown by a chute of air to make them appear as if they were flying.
Revealing mistake: In the scene where they are on the plane, right after the old women comes out of a stinky bathroom, you can tell it's not the back of David Spade's head when he goes in for the 3 sec change. (01:16:00)
Revealing mistake: When Tommy runs into the glass door after a successful sale, he leaves a mark on the glass, clearly from makeup for filming, not just an oily face.
Answer: A number of online explanations said it was because Lowe was already contractually tied to another project while this one was being filmed. Another explanation is that he was left uncredited so his appearance mid-film would come as a "surprise" when the plot took a different turn.
raywest ★
I read where his contract with the mini-series "The Stand" left him unable to take any credited roles. However, it seems "Tommy Boy" began filming after "The Stand" aired and he was credited for his role as Jesse James in "Frank and Jesse." However, it seems to be an Internet story where the source isn't credited.
Bishop73