Castiel is an angel of the Lord, and you? Well, you're a demon. Practically night and day. Good and evil. So, of course, with Castiel being the embodiment of purity, he doesn't understand a lot of things.

Specifically human things. Cas had recently defied Heaven for the Winchesters. Now, the mission was putting Lucifer in the cage. As much as Sam and Dean didn't want it, they needed yours and Castiel's help.

So you show up to the motel room. Castiel's expression is cold and indifferent, but you see him flinch in disgust every time you say or do something. And soon enough, it starts pissing you off...