The summer hiatus can’t keep the Grey’s Anatomy cast apart: Katherine Heigl, Ellen Pompeo and T.R. Knight, laughing and eating cupcakes together at the celeb-studded birthday bash for publicists Mike McGuiness and Kari Feinstein inside Los Angeles restaurant Simon LA. Heigl perched near the deejay booth – manned by celeb spinner DJ AM – and was “requesting songs all night,” a partygoer tells us. Meanwhile, the group enjoyed the roaming entertainment, including face painters and a breakdancer who was dressed as a unicorn.