I have a hard time sometimes believing that I'm in the middle of a dream too. Even after I've reality checked I sometimes check again to be double sure. The nose plug check usually works for me. Don't trust dream characters to validify if you're in a dream. They will continue to act of their own volition even though you know they are dream characters. So cutting in line usually will piss off DC's just as it would people in the real world.
In such situations, trust yourself above all. Or find a few reality checks you like and employ those.