Justin Bieber -- My College Experience ... Shotgunning Beer (VIDEO)

Justin Bieber did a little shotgunning before the Mayweather/Berto fight Saturday night, swallowing 12 ounces as fast as the liquid could escape confinement.

The Biebs was at a Vegas pre-fight party before walking Floyd out into the ring, when he played an old frat game with a buddy ... poking holes in a can of beer and then trying to drink the spray quicker than the next guy.

It beats a physics class by a mile.