Fencepost, this one's for you:

A brain surgeon called a plumber on a Sunday to fix a leaky faucet. The plumber changed the washer in 2 minutes and handed the doctor a bill for $200.

Doctor: This is too much, I don't even charge that much for 2 minute work...

Plumber: I know, I used to be a surgeon too, that's why I'm a plumber now!