Look out, Hollywood A-list bars and trendy hangouts! The Shannon Twins are 21 now and can hit the town. Former Playmates and Hefner girlfriends Karissa and Kristina Shannon celebrated being old enough to drink with a night of partying Friday in NYC, starting with champagne at Via De Vile before ending the night at the Greenhouse. Not surprisingly, former friends Spencer Pratt and Heidi Montag weren’t invited, since Karissa claims the pair swiped her sex tape. That didn’t stop her from selling the racy vid to Vivid for some big bucks. Happy birthday, girls!