When I used to work in the movie theater game, we had a guy who'd come in that we'd refer to as the "phantom masturbator". He would find a woman seeing the movie by herself, saunter up to the seat next to her and start masturbating during the film. She'd notice him, and he'd run out one of the side doors to the alley. We never had security cameras over there, so we could never see who the guy was. I'm sure he's still doing it to this day.