A old man vacationing in las vegas decides to visit a brothel,as it has been a long time since he's had any. After paying the mandam, he picks out a cute little blonde girl and they go upstairs. After the preliminaries, he climbs on and starts going at it.
He hollers out "How am I doing, honey?"

She repliers, "About three nots."

He says, "Three knots? What does that mean?"

She says, "You're not in,you're not hard, and you're not getting you money back!"