Think R. Kelly is the reigning king of bootylicious sex jams? The Philadelphia/Brooklyn-based rap group Spank Rock might make you reconsider. MC Naeem “Spank Rock” Juwan, who sounds like a young Q-Tip, spits sexed-up lyrical tales about cock-teasing dancers (“Backyard Betty”), flirtatious pickups (“Touch Me”) and straight-up booty-shaking (“Bump”). With…