"Former Doctor" joke

A pipe burst in a doctor's house. He called a plumber. The plumber arrived, unpacked his tools, did mysterious plumber-type things for a while, and handed the doctor a bill for $800.
The doctor exclaimed, "This is ridiculous! I don't even make that much as a doctor!."
The plumber waited for him to finish and quietly said, "Neither did I when I was a doctor."