It didn't take that long for Castiel to get drunk, but then, Castiel couldn't remember how many beers Dean had talked him into downing. Neither of them really cared - they were both wasted, they were both going to have a hangover in the morning, and they were both going to do some really stupid stuff. (Or at least, Castiel had hoped.)
It started when everyone else left, Castiel picked up his backpack and was halfway out the door when Dean appeared behind him. "You're drunk, Cas," he told him, "You can't go home like this. Stay here." Castiel didn't say a word, but walked back in, closed the door, and giggled, "You're drunk too, you know."
Then they both collapsed on Dean's bed, holding each other in a perfectly innocent fashion.