Chris Brown -- Prison Schmizon ... LET'S PARTY!!!

Chris Brown didn't let the threat of 4 years in the big house get in the way of a big night out in Hollywood Monday ... because Chris partied like a rap star at the Playboy Mansion.

Brown -- whose probation was revoked Monday afternoon in the Rihanna beating case -- mugs with 2 cute chicks at a charity event to celebrate the MLB All-Star game.

Chris hung with Snoop Lion and L.A. Dodgers phenom Yasiel Puig (fast becoming a Hollywood party animal).