Floyd Mayweather learned the hard way ... you drive on Brittney Elena, and you WILL get blocked!!
The boxer was playing The $50k Charity Challenge celebrity basketball game at UCLA on Tuesday -- when he got posted up by the smokin' hot "Wild 'N Out" model.
Turns out, Elena has SERIOUS game ... and when Floyd when up for a shot, she packed him up good.
Floyd wanted a foul call -- he didn't get it.
Mayweather played pretty well for the most part -- aside from being CROSSED UP by R&B singer Tank.