A man picks up a girl at a party. They proceed to her place and things are starting to heat up. He takes his shirt off and washes his hands. He takes his pants off and washes his hands again.
The girl says to him: "I bet you're a dentist."
Surprised he says: "That's correct, how did you know?"
"You washed your hands a few times, so I figured you're used to it."
After a few hours of playing around, she says: "You know what? I'm willing to bet you're a very good dentist."
"How can you tell?" he asks.
"I didn't feel a thing..."