When you're stroking a person's dick (they're on all fours), and right as they're about to cum, you
yank on their
balls like you'd yank on a cow's teat, and they "mooo!" in
pain.
I gave a guy the funniest blue
balls the other
night, both figuratively and literaly; hit 'im with the dairy maid.
The amount of therapy he'll need after that
night is gonna be expensive, but his reaction was priceless!