"Do we have to know this?" is probably the most aggravating question students ask in class—though maybe we could have a contest.
"Can we do extra credit?" (if stated around the time of final examinations) comes to mind, too.
In fact a generic subset of questions that are already answered clearly on the syllabus might have its own category.
But a big one is "Did I miss anything?" when the individual did not attend a previous class, for whatever reason. If any question brings out sarcasm in response, even with the most genteel of instructors, this is it.
"Well, we had a bonfire, and then sacrificed goats and ate their livers raw and danced in the skins. But you missed it, Dude!"
"We had free pizza and played Grand Theft Auto VI. Sorry you weren't there!"
"You and your kind must be punished severely. Smithers! Release the hounds!" (with a nod to Mr. Burns on The Simpsons).
David Hildebrand teaches philosophy at the University of Colorado at Denver. His blog has an interesting response to the question—more thoughtful than goats, hounds, and pizza. If you click around, the site also has some interesting perspectives on the place of humanities in today's technology- and career-driven higher education environment. You can check it out here.