Bruno Mars literally sang for his supper at The Darby restaurant on West 14th Street the other night. While having dinner with friends, he left the table to jump onstage with the band and serenade the house. According to our spy, “The crowd went wild, singing along” while Mars performed his single “Grenade.” He used his leftover energy to party at 1Oak, where he held court at a VIP table with fellow music star Usher, and at SL in the Meatpacking District later that night.