What you answer is largely irrelevant, they observe how you answer. Whether you lie, tell the truth, make a joke about it or say you can't think of anything, you can do any of those the wrong way or the right way.
The question will make you think about what you fear, even if only subconsciously. That is if there's anything in particular you fear, if not then the question still may make you insecure and overthink what to answer.
So to answer your question, the best way to respond is with confidence and fearlessness. If you want to you can do this without even uttering a single word, as long as you nail the right facial expression and body language, that's what they actually look at anyways.
I'm sure we all have experiences where we have observed two different people saying the exact same things and getting wildly different responses. If you pay real close attention you'll see that the difference comes from how it's expressed. How you present something has a HUGE impact on how it's perceived, it's said that the words themselves only account for 7% of communication.
Actions speaks a lot louder than words. If you want to improve you should look into your overall expression. If you don't want to micromanage your muscles you can take a look at the source of your expressions, which is your emotions. If you feel like a fvcking king you will most likely act like one too, without even thinking about it. Almost anything you say will be positively received.
If you feel insecure it will most likely leak out through your overall expression and women pick up on that really easily, they're attuned to reading expressions. No matter what words you use it will probably be received negatively.
It's not about the words, it's about expression. I urge you to look into improving that area of communication long before even thinking about what to say.
