Almost 30 years later, this is still one of the funniest scenes on film:
There is something innocent about Porky's (trailer here), despite the subject matter. I think it has something to do with being released before the PG-13 era, which hyper- sexualized everything for younger and younger ages. As long as actual nudity is avoided, anything's acceptable in a PG-13 film. Porky's, with all its nudity and crudity, is somehow less corrupting than your average modern day teen flick. Maybe its because the film didn't take it all so seriously.
It's just fun, and therefore funny. At least, it's funnier than 90 percent of the movies I've seen in the last 10 years.