Dean froze when he heard the sound. That and the words the man spoke made it easy for Dean to guess what he was dealing with. Maybe he was being paranoid, though that is what had kept him alive for so long; however, if he ended up teleported to some warehouse or whatever in South Dakota again he was going to be pissed off. He didn't know who this was but Dean was willing to bet it was an angel. Yes, maybe paranoia but it really hadn't been all that long ago since Uriel had said something almost similar and whisked him away. And Cas liked to do the entire 'we need to talk' thing. Which led to him being talked at about shit he nothing to do with.
And they all had this tendency of grabbing at his shoulder.
Dean took a small side step to move out of this angel's reach. He knew that he wouldn't be given a choice but that didn't mean he'd agree to it.