Dean waits for the kiss to break naturally, and then he draws away, hovering just above Cas's mouth; the grip in his hair tightens enough to keep Cas from following, and then Dean breaks into a slow, mocking grin.

"Man, you fell for that easy. How pathetic are you?" The hand in Cas's hair twists, holding him painfully as Dean keeps Cas pinned under him, but now it's all strength and aggression.

"Are you that horny, or that hung up on," he glances down at himself and back up, "this guy? Either way, you should give it up. Who do you think you are? You kicked him out twice; you think he's ever going to want to come back, even when this is over? He's never going to want you now."

He lets that settle and then somehow manages to widen his grin.

"And that's before I'm through with you."

Dean's head tilts back, and suddenly he's a Leviathan, mouth open and ready to devour Cas as he leans back down for the first bite.

Cas will wake up before the Leviathan version of him ever manages to sink his teeth in, but it'll be close.