"Are you okay?"
"Yeah, it's just my Tourette's."
That's a question I ALWAYS get, either as a verbal question or as a concerned (or standoff-ish) look. And that's EXACTLY how I answer.
Now, this can do one of two things: Shut them up or encourage them to ask more questions, both of which I've encountered, though the latter is what tends to happen more frequently, which is really a good thing because it shows interest ...