Gabriel needs to let off steam. He's been stewing in varying levels of exasperation for a while, and while Christmas at Castiel and Dean's is definitely helping him stay calm, he still needs to do something to unwind.
And he's fairly certain that killing humans is still more than a little taboo.
Not that Gabriel is really concerned about either of them when he takes a seat just far enough away from the pit to avoid the fire.
He'd like to close it completely, permanently if he could; but he doesn't want to start a war. And really, the demons are asking for it, the way they're all flying out like that. It's too easy to kill them, and could be seen as an attack anyway.
But sending them back...
Gabriel snaps his fingers and watches as the smoke swirls back into the Pit, giving it a moment and letting more pour out before snapping again and sending them back again.
As pastimes go, it's not bad, he figures. He might even do the rest of the Gates, if he can track them down.