This ties in well with the discussion about Dean not owning his body for most of his life, always belonging to other forces, and being marked by them in all sorts of ways. If so - and I feel that it is so - being marked again would be... something to discover and work through feelings about. For pretty much the first time, for about a year now, Dean has owned his own body and his own house (sort of), his own room. Not owning himself all over again must take him back, in a bad way. Perhaps it's comforting, he knows how to be that way. Perhaps it's punishment for himself for taking Sam's agency away, or even for enjoying his new status and getting comfortable.

this gives me lots to ponder, lots of thinky thoughts, also lots of kinky thoughts about Sam owning Dean's body and pretty collars that match his eyes and such...;P