Continuity mistake: When Billy is in first grade, Miss Lippy sits all the kids down in a circle for story time. One little girl goes up to Billy and says, "You have a mis-shaped head.", while she stands in front of Billy. In the very next shot, you see her stepping over Billy's leg to sit in front of him.
High School Principal: Mr. Madison, what you've just said, is one of the most insanely idiotic things I have ever heard. At no point in your rambling, incoherent response, were you even close to anything that could be considered a rational thought. Everyone in this room is now dumber for having listen to it. I award you no points, and may God have mercy on your soul.
Billy Madison: Ok, a simple "wrong" would have done just fine.