What I got from this movie: People are not who you make them out to be

We spend a lot of time building up ideas of who people are. In Dennis's mind, Beth was this perfect girl. But in reality she was much different. Just like Cammy wasn't who Rich thought she was. Rich didn't even know who he was. The theme runs though the whole movie.

Beth: "Wow. Look at the sun. So big and pretty."
Dennis: "That's an optical illusion."

All people are optical illusions. Do we really know anything about anyone? That's really the theme of the movie. Deeper that your typical high-school comedy.