Dumb Question

Student to me: Can I call you by your first name?
Me: Excuse me? (giving him a chance to say "just kidding")
Student: Can I call you by your first name?
Me: That is a dumb question.
Student: What, why?
Other students piping up: I thought there was no such thing as a dumb question!
Me: That's true for most questions. But that is a dumb question.
This student had been slacking in the past few weeks, so the chance to legitimately insult him was satisfying. Plus, his question wasn't serious.

I called his parents later that week and kept him for detention because I was tired of him wasting my time, and can I tell you, this week, he has been a work machine. I'm calling another parent today, and I hope that works out just as smoothly.