Probably "The Last American Virgin" for me.  It seemed like such a goofy teen sex comedy until the end.  Absolutely heartbreaking.  It's not a great movie, but it changed the way I think about relationships.

My wife just - out of the blue tonight - referenced the Time of the Apes episode. She was filling the sink with soapy water and said, "Water, the source of all Sandy Frank films." When I laughed she followed up with, "It's fun when you're smart!!!"

Couldn't agree more on Freaked. I even went back and re-watched Bill and Ted after seeing it; but Bill and Ted still sucked.