When the demons started smirking, Dean knew for certain that he wasn't going to end the knight without his face busted up a bit. It wasn't that the demons didn't smirk. Demons were over confident as in general. However, when a hunter started making demands and they were all cool with their smirking, you knew that they were more than a little in over your head. And seeing as Dean had already gotten that part of the memo, the situation didn't settle any better with him.
It didn't help that had to control himself from shooting Sam another look with how he was demanding things. Did he really think that they would answer? Sure they'd made it this far, so they should give it a try. But Sam just seemed a little ... unstable.
When one of the other idiots went after his brother, the fact that he knew that Sam couldn't take care of himself didn't stop Dean from shooting rock salt at the demon. "We could do this all night. Were the questions too big for you? How about we start small. Starting with what the hell are you doing here. A bunch of demons, meeting up in a deserted building ... You have to be up to something." Dean stated, as he aimed his gun at the leader.