A man goes into a dentist’s office.
Man: “Excuse me, can you help me? I think I’m a moth. “
Dentist: “You don’t need a dentist. You need a psychiatrist. “
Man: “Yes, I know. “
Dentist: “So, why did you come in here?”
Man: “The light was on. “
This joke is included in the Black Book of Jokes. You can order it from here.