"Goddamn it all to hell." Nevermind that Dean had met THE Gods here, that he had been to Hell, this time he meant nothing by his words other than pure frustration. How was he supposed to argue with that? It had been that sort of reasoning that allowed him to cave in the first time when she wanted to go after Alastair, but this was different. She didn't just want to be part of the huge army looking to kill the bastard, she wanted to go and actually fight to find him. She wanted to let RUBY of all things take control of her body and puppet her so that Ruby's demonic ability to survive wounds and her knowledge of hell combined with Claire's ability to heal would--
Would what? What was she going to walk into that made her think both powers were necessary? Dean didn't even want to think about that....especially because he knew he was fighting a losing battle. He could argue the specifics, lie and say that no matter what happened to coma girl's body, Ruby could go to hell for all he cared, but Dean knew he'd just be wasting time. He also knew time wasn't on their side.
Claire's mind was made up, but, worse than that, her reasoning was too similar to Dean's to ignore. She had to do this, and, because she was his best friend, he had to let her, no matter how much it just felt wrong to think about the black smoke going into the body of the girl he had come to trust and care for so much.
"Goddamn it." He was repeating himself, and he was going to lose. Nice, Winchester, really nice.