Offset reacted to a guy spraying champagne -- which might have splashed Cardi B -- by delivering some cham-pain ... in the form of a wild punch off the stage.
The husband and wife rappers were partying after 3 AM at Booby Trap On the River strip club in Miami, and were standing on stage next to a pole when the champagne started flying.
We're told Cardi got wet and wasn't thrilled about it, but Offset was enraged and immediately began looking for the guy. As you can see, once he spotted him, Offset wound up his fist and let it fly.