I knew Morton Feldman
I was a teller at Morton Feldman's bank in the mid-80's. Usually his harried young assistant (she might have been a student, but the impression I got was that she worked for him at the University of Buffalo) would come in to do transactions for him. Occasionally he would come in himself. One day, she came in, was waiting in line - a minute later he comes in. Feldman sneaks up behind her and gooses her. She gives a shocked yelp. Instinctively twists around to see her attacker. He is grinning, chuckling like a boy, his big frame shaking. "Who'd you think it was?!"