Oooh, I wasn't thinking about it like that. Actually, I think Sam would probably welcome a quip like that from Dean - it would show that he's still got some of his "old self" there. At the moment I think Sam is too worried about Dean to be thinking about their past argument (and it's curious that even though Sam has said they couldn't work as brothers he's been the one to work in their usual brotherly fashion). If Dean was himself he would have perhaps looked and smiled at Sam on that line and Sam would have given his patterned bitch face. As it was, there's just too much angst between them to be as light as that *sniff*

Ties into the "I know, you wouldn't have done the same for me", which is perhaps the most crushed thing I've heard from Dean in ages.

That was so painful. It obviously cut very deep with Dean - he clearly believes it, even though we (and Sam) knows it isn't true.