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!