Once had a man stand next to a me and start mumbling that the metal rail was nice and solid, and he would pay up to $5 for it. He became more and more enthusiastic about the rail and its quality, and eventually began beating his head against it until he began to bleed. I couldn't get out of the seat because there was a crazy, bleeding man blocking me in. Fantastic!
Also have seen: nose picking, booger flicking, fingernail clipping, toenail clipping, vomiting, used condoms, and someone hock a loogie and spit it onto the floor of the train. After spending a half hour on the train to get to work, I usually feel like I need to be hosed down. However, after hearing tales of NY's subway system from my brother, I feel blessed that it's as tame as it is.