I’ve been noodling over this post for the past few days, and I think it’s almost right, in that Dean throws out the sexual barb because he almost certainly knows that he’s Cas’s weak spot.
And yet… I think the person Dean’s really digging at here isn’t Cas, but himself. He’s the one sexually attracted to Cas: he’s the one who can’t stop looking at Cas’s lips, who always looks so uncomfortable when Cas crowds his personal space. And Dean hates himself for it, because he knows that this is an angel of the Lord, the holiest of the holy, and he—well, what is he? He’s the blood-stained fuck-up, the man-sized hole of Daddy issues and neediness, the demon who never deserved to be saved from the Pit. What business does he have feeling something so dark and needy and human about an entity as good and heavenly as Cas, someone who so profoundly believes in Dean’s non-existent righteousness, who talks about him in terms of “special” and “saved” and “profound bond”, who rebelled against the divine plan and the entire Host of Heaven, and sacrificed everything, just for him, all for him? Dean knows it’s disrespectful, this dark and small and petty human sexual attraction, he knows it’s wrong and unreciprocated and he wishes he could make himself stop but he can’t, he just can’t.
Remember what the Dean!Leviathan says about Dean? “He doesn’t have relationships; he has applications for sainthood”. For nobody is that more applicable than Cas (which is why Cas’s eventual betrayal hurts Dean so much). To S5!Dean, Cas is a concept, a creature so innocent and pure Dean didn’t even think it existed until it saved him from eternal damnation.
So when Cas revokes his faith in him in that second GIF; when Cas says, essentially, “you are no longer worth my faith in you”, that’s when Dean snaps, because that hurts so much, too much, and all he can think to do is lash out with the one thing he thinks will hurt the most — except he doesn’t stop to wonder who he’s really trying to hurt here.
That’s why, when Dean says “Blow me”, Cas seems more confused than anything else — he can tell that Dean is angry, and he’s angry too, but more than that, Cas doesn’t understand why Dean chose to express himself with those specific words.
But to Dean, the innuendo makes perfect sense; it’s a form of self-harm, of self-torture. In the same way he bitterly tells Kevin (twice) that angels are “junkless”, it reminds him of what he wants but can never, ever have.
Because Dean trained under Alistair, he knows all the best ways to torture a man, to make him break, and deep down he knows that what he feels for Cas is what will break him; or, more specifically, what will break him is that Cas can never feel what he feels, that angels just don’t have the equipment to feel that way, that whenever they try, it just breaks them apart.
And I eagerly await the day Dean realizes he was wrong.
