His grip tightens on Stiles' waist, he grins, and Derek licks over the bruise blossoming on Stiles' neck slowly, carefully, savoring the salty taste of skin and sweat. He's going to have one hell of a hickey, tomorrow, and Derek can't really bring himself to care. He draws his lips up to Stiles' mouth and kisses him deep, licking into his mouth hotly, pressing his own forming erection against Stiles' hipbone.