Matt Barnes had the best weekend ever -- rounding up some of his famous friends and teammates to party with hot bikini chicks ... and it was all for a really good cause.

The NBA star and Snoop Dogg teamed up for their annual Athletes vs. Cancer charity football game in L.A. -- but before the gridiron sesh, Barnes and his Warrior bros Draymond Green and JaVale McGee hit up Beverly Hills for the pregame pool party.

It all went down at Tai Lopez's mega-mansion where stars like Demetrius Shipp Jr. (aka movie Tupac) kicked it with James Harden, Reggie Bush and celeb photog Facet, who rolled deep with a squad of beautiful models.