Know what's the worst? Finding out very quickly someone you might be into is still into someone else. Nothing quite like immediately feeling like you're going to be the forever second fiddle and have an unrequited love with someone who has an unrequited love with someone else.
Know what's even worse than the worst? Telling someone you want to make them a parent. Yeah, don't think I'll be sleeping with you. I don't care how much birth control methods I see you employ, I won't trust any of it.
"You don't say? Well, as long as we're being honest about the future, here's what I see. I can see myself telling you I have to use the bathroom, secretly calling an Uber, ditching you and then blocking you from my phone and all social media."
"This date has gone better than I could have expected. I thought we'd just have a nice meal and have some pleasant conversation. But instead, I'm getting a free psychoanalysis from a clearly qualified expert. Swell."
What's the end game of asking this question? You think if it's a lot you stand a better chance? Your only real shot is if they have severe O.C.D. and want to change their number from an odd to an even.
Look, we all have several regrets. Reliving them isn't exactly fun, especially in front of a potential future significant other. Maybe you can ask someone this on their death bed, but even then, probably don't.
Confidence is the single most attractive trait anyone can have, whether it be on a date or a job interview. Know what destroys the illusion of confidence? Constantly asking how you're doing along the way. Just assume you're great. It may make you seem kind of douchey, but hey, dating isn't supposed to be easy.
On the flip side, don't call someone out for seeming nervous. They're doing their best. Maybe try to help put them at ease. Know what doesn't put them at ease? Letting them know their confident facade is utterly see-through.