It all started when a valet and a paparazzo (not ours) ... started yelling at each other ... and the valet straight up BITCH SLAPS the pap right in the face.

The pap drops his gear and goes after the valet ... and during the melee, they knock into a man and his date ... who had just finished dining and were waiting at the valet stand.

The male patron flips out ... and unleashes a fists-of-fury style beatdown on the photog ... while his date calmly gets into the waiting car.

After the pap runs out of steam, the patron moves to get into his waiting Mercedes ... but not before yelling out one final taunt.