MLB Star Brian Wilson -- I'M A SAVAGE

L.A. Dodgers pitcher Brian Wilson snapped over the weekend ... into a Slim Jim ... 'cause he dressed up as the Macho Man Randy Savage for a humongous celebrity-filled Halloween party in Bev Hills.

The place was packed with famous people -- like Larry David (who dressed up with another guy as Siamese twins), Hilary Duff & her NHL husband Mike Comrie, David Spade, Cindy Crawford and more.

Wilson eventually left the party with a super hot mystery chick.