An old retired submarine sailor puts on his old uniform and heads
for the docks once more for old times sake.
He engages a prostitute and takes her up to a room. He's
soon going at it as well as he can for a guy his age, but
needing some reassurance, he asks, "How am I doing?"
The prostitute replies, "Well old sailor, you're doing about
three knots." "Three knots?" he asks, "What's that supposed to mean?"
She says, "You're knot hard, you're knot in, and you're knot
getting your money-back!