Rihanna had a damn good reason to hit the Hollywood club scene last night — she was finally attending her long-delayed 21st birthday party … complete with loads of booze, a couple of decoys and NO Chris Brown in sight. Sources tell TMZ the whole thing went down in a private patio at Coco de Ville. We’re told a five-person party ordered everything from Grey Goose to Jack Daniels, a round of “fun” shots, some champagne, and a cupcake tower for the birthday girl.