Cas + open
To say that Castiel was having fun while his house was full of people would probably be a strong exaggeration, but he was managing. He'd yet to feel so overwhelmed that he'd needed to go hide at all - considering it more polite to excuse himself and take a moment to just to breathe while staring into the bathroom mirror instead of escaping completely into the comfort of the tree house.
If he went there, he knew he probably would find an excuse to not return until Dean called him back.
Still. It wasn't so bad, and he did know a good number of the people here. He smiled politely, sipped his champagne (Dean may not have drank anymore, but apparently enjoyed living vicariously through the fast metabolism and tipsy-ness that Cas managed) and cast the occasionally glare at wonton wrapped mozzarella sticks. They were offending him on a personal level based on the fact that they were deep fried and completely unhealthy.