I always wondered why a sexual comedy film would be called American Pie. I mean what is the significance of "Pie" in the title?
This is answered pretty well on the Wikipedia article. Specifically, the last sentence in the quote below.
The writer is using "pie" as a metaphor for your first sexual experience. When you read the title "American Pie," don't think of it as a delicious desert, but rather as a sexual innuendo.