I've been fascinated by understall wanking ever since, and wished I'd had the guts to let him pull me off. Instead, i panicked and left as quickly as I couldn't.
I went into a department store toilet for a wank and the guy in the next stall must've seen the shadow of me stroking my cock. He put his hand down and gave a beckoning motion. I'm a straight guy and didn't know what the hell was happening. Next thing, he was peeking under the divider.