Old retired sailor
An old retired 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."
She says, "You're knot hard, you're knot in, and you're
knot getting your money back
.