Rihanna Plays 'Just the Tip' ... for $200

Rihanna knows EXACTLY how to please a man ... especially if that man is a waiter, because on Friday she gave one lucky server in Hollywood the biggest tip of his food-slangin' career.

It all went down at the Laugh Factory comedy club -- Rihanna was there with 6 of her friends ... downing drinks and listening to Dane Cook tell "jokes" on stage.

But when the bill came ... a measly $80 ... we're told Rihanna asked her waiter what the biggest tip he ever received was. He said $100 ... so Rihanna slapped $200 into his hand and replied, "Now I'm your biggest tip."