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: He was the fat kid. I was teased in school for being the nerd who wore glasses and read books.