"I really, really hate you," Dean says, and sounds kind of chipper about it, so apparently this is worse than Sam originally thought.

And Sam originally thought it was pretty damn bad, you know, all things considered. It's dark, and it's hot, and there's a serial killer of the chainsaw wielding variety on the other side of the door that they can't open, and they're in a closet of all places. And really, he's not sure which of those things is worse.
Bwahahaha.
Such a Sam/Dean moment! Hee.