A crusty ole biker walks into a bar to have a ice cold beer after a hot, dusty ride.  Down at the end of the bar, he spies a mighty fine looking chick in a sailor suit.  She heads his way, smiles and asks if he's looking for a good time. Realizing she was hooker and since it had been quite some time since his last romp in the hay, he started up negotiations.

After agreeing on a price, she escorts him to her bed room and they start going at it. After about 20 minutes of humpin & jumpin the ole biker looks her in the eyes and asks:

"So babe, how am I doin'?"

She replies: "You're doin' about 3 "knots".

"3 knots?.... What's that mean?" replies the biker.

She said: "You're NOT hard, you're NOT in and you're NOT getting your money back!"