I will start with a couple of personal ones ive had.
My best one was during a trip into town after a night, hungover wearing grey trackie and commando. It got alot of stares but i noticed these two girls talking and laffing as i walked into mcdonalds. I paid for my food and was walking out and saw them walking straight towards me. They both stopped and said "boxers are fairly cheap but seriously can you fit in them" i was really embarressed and they both laffed and then went " but seriously that is unreal" and just walked off giggling!
Another was while i was in high school, one of my girl mates would always ask me how i fitted into my school trousers, dont know why but it was amassive turn on.