More or less literally, raising one's eyebrow in disdain. Often this is combined with raising the nose and chin as though smelling or seeing something offensive. Used to express contempt and superiority.
Lord Cyril expressed his low opinion of Reggie's Socialist rant with a supercilious sneer.
Supercilious means full of arrogance and acting like one doesn't care at all and is indifferent, as if that person is a royal King or Queen.
In the ingeniousSAT prep book "Up Your Score" the example sentence for supercilious goes: "The supercilious person said, "I am perfect, but you are a super silly ass."