Oh, so many times, I'm almost embarrassed to admit.
One in particular. As an early teenager we were watching a Sex Education Film in CHURCH, of all places. And at the point where a male erection was being described and graphically diagramed on the screen, my buddy and I just absolutely LOST IT, man. We literally ended up on the floor, completely convulsed and debilitated with helpless laughter. The adult instructors were not similarly amused. At all.
Ah, good memories. Inappropriate? Sure. But I gotta say, all these years later, I can't help but laugh out loud even now as I write this "confession"!