Fat Joe and his buddies closed down a legendary NYC restaurant, but the busboys kept the party going ... and he thanked them with a fat gratuity.
The rapper grabbed dinner at Rao's in Harlem Wednesday night with bail bondsman Ira Judelson and DJ Shortkutz, and after all the other diners had left ... the busboys went to the jukebox and blasted Joe's "All the Way Up."
We're told he loved it and launched into an impromptu jam sesh with the entire waitstaff, so naturally they cranked up "Lean Back" after that.
Joe stuck around to take selfies and chat with everyone before picking up the $300-400 tab ... and leaving a few hundred bucks for tip to say thanks for the turn up.