You're on a date and you feel its going well. Then, all of a sudden, everything changes.
Why? Because your date asked you 'That' question: "Why are you still single?"
So how are you supposed to answer it without sounding defensive, offended or sad?
Well it's easy, and it comes down to these two parts:
Part 1. Be prepared: its a terrible question to ask on a date, so don't ask it. But you can't stop someone else from asking it. And just because they're asking it doesn't mean they're a bad person or that they're not interested in you. So don't worry about it, but do have a few stock answers prepared that you're comfortable with, such as: 'I've just not met the right person yet', 'I'm really enjoying meeting new people right now', or even something humorous: 'Because you haven't proposed yet', etc... but keep it light and positive.
Part 2. The pivot: while getting asked this question doesn't have to be a date-breaker, spending the whole date discussing it likely will be. So before that happens, ask the following back: 'How about you?'
Why ask them the same question? Because, yes, its a lousy question to ask on a date, but its also a really interesting question to ask back if someone else has asked you first. The key is not to dwell too long on it; once your date has answered it, move on to another subject - talk about some things you both share, or a funny travel story, or ask them what they love doing most in their spare time & why. Once your date is back on track, ask for a second or third date... if those go well, the answer to 'Why are you still single?' might soon be 'I'm not anymore!'