I was at a crowded party once, stuck talking with a guy who was quite full of himself. He was bragging about how well he played guitar, and bass, and piano, and added, "and I'm getting pretty good at the harp," putting his hands near his mouth to show that he meant harmonica, not the stringed instrument. After he made the hand gesture, my friend Jeff, a musician himself, silently reached into the front pocket of his jean jacket for a small harmonica, offered it to the big talker and said coldly, "Prove it."