Most Unexpected
Since every human is equipped from birth for nudity, I felt I should focus on the "unexpected" aspect of the question.

That still leaves quite a few choices of experience to relate: the mule train surprising the nudists at the wilderness hot spring; the french foreign exchange student at the pool; catching my wife and my mother skinny-dipping?

Nope, the most unexpected was back in high school. I left my friend Mark alone in my room while I went to pee one evening. I don't remember why he was there, but we were likely going somewhere (I had a car).

I returned to find my door closed - opening it I saw Mark lying back on my bed, pants at half-mast, furiously stroking his cock. The visual is still burned into my mind these 35 years later: the curly reddish-blond pubes, the slight curve to the left, and the intense eyes-closed look of concentration on his face.

I must have made some sound - he looked up, stopped, then said "Hey, don't you knock?"

I closed the door quickly, and went into the kitchen. Mark appeared a few moments later, said "Um, sorry about that," and we've never mentioned it since.

Still, What The Fuck? "Don't you knock"? Not when it's my room and I go out for a 2-minute slash. No - I don't knock!

Pass the brainwash,please.
(danalan Pretty good, for an amateur., Sat 30 May 2009, 3:53, 1 reply)

The slight curve to the left.
Phew, I'm not the only one then!
(SonoraAeroClub "OH SWEET HELEN OF BALLS!", Tue 2 Jun 2009, 15:33, closed)