For one of our undergrad classes we used to have to conduct experiments that broke social rules. One of them was staring with people in the elevator or getting really chatty despite their rising discomfort. It really was funny.
One of my male friends dressed up as a girl one Hallowe'en and showed up to his university classes. He actually was quite a pretty girl. He had a slight frame, nice legs accentuated by black pantyhose, a dress to just above the knee and a blond wig. He got in the elevator with a male classmate who did not look up right away. When he did, he did the slow travel up the legs gaze and when he got a little further up was mortified to realize that the object of his Peppy Le Pew like amorousness was indeed male. He was so embarrassed he blurted out, "I'm sorry man, I had no idea. I'm really sorry!" and got off the elevator at the next stop!