It really depends on how much they do it, and what talking about an ex (or exes) does to their demeanor.
I pay close attention to such conversations. Much can be learned about a person by listening to them talking about an ex. If they do it incessantly, and with rancor, that's a pretty good sign for me to bail before things go any farther.

Not on a first date please.

I guess it depends on the context. If she's obsessed with her ex — what a dirtbag he was when they were together or what he's up to now or how great he was in bed, said wistfully whenever we're intimate {grumble, grumble} — that's a red flag that something's up and she's not fully present in our relationship. But if she merely says things about him in passing, like "Oh, when X and I went to Paris, we visited the Louvre" or "X could be abusive sometimes, though I didn't recognize the pattern at the time," then I'm fine with it. I figure her past made her who she is, so I can't expect, and shouldn't want, her to ignore or hide her past relationships.

Never a good idea to bring it up early on, but it can be theraputic and helpful for mutual understanding later in the relationship. It is important to speak in terms of what the past relationship has taught. Involves understanding and Self discovery, learning from past mistakes and Moving Forward to a happier and healthier life. Never good to be stuck in the past.

It depends on the situation.

Depends on the context.

If she says, WOW, Whew! my ex never did THAT to me before! Is that even legal in this state?

I'ld be ok with it.

When they're crying on your shoulder about their ex, they are revealing who they really are, warts and all, so grab that bottle of wine and LISTEN UP!

This is a huge red flag for me. I refuse to date someone who isn't over an ex.

If they blather on about the Ex..fuck that..shows they're not over it..I don't have time or the patients to hold someones hand...

I think that the last thing that anyone would want to hear on a first date is someone who talks about their ex-whatever. On a first date it would seem to point to a "baggage issue" and might serve as a red flag.

Small doses.
I don't want to hear it much, and I certainly don't want to be compared to him.
It's pretty rude IMO.

If it's just a reference point then it's ok, but if it turns into an all night ex rememberance affair then it's pretty rude. If someone constantly mentions their ex on a date, they obviously aren't over them, or they are just really inconsiderate and aloof of the situation. Either way, we don't need to keep seeing each other. If her response to every issue I bring up is, "Oh my ex did that!", or "My ex used to do it this way!", or something similar, then it's a huge turn off.

My vote was 'I don't mind at all'. with the caveat - as long as it is not the blame game.

It isn't an ex; it is his deceased wife. I don't mind at all. Those 21 years are a part of who he is. It shows me he can commit long-term, love deeply, feel emotions, and trust me enough to share. I hope her and their pictures stay up to include her in his present life. He's not living in the past, He's living with the past. I'm one fucking lucky girl! ?

Pay attention, you might learn a lot! Think of what they are saying as if you were reading a real estate ad: example, "conveniently located" =next to a 24-hour liquor store. Etc.
Nobody just landed on planet Earth....your past is what makes you who you are today
90% chance they will treat you the exact way they treated their last lover. Pay attention!

It depends on how much they talk about them and HOW they talk about them. If there is a huge amount of unresolved anger, or disrespect then it is a red flag. I talk about my ex because I still see him fairly frequently, the kids like to do family birthdays and holidays. We're amicable. I am not angry with him, I am pretty indifferent, I think. We spent 25 years together and have kids and grandkids, we are linked whether we like it or not.

Hearing someone rant and rave about their ex gives me good insite on what bothers them. Sometimes it's good, sometimes bad. After that, definitely small doses. It gets annoying. And never compare your ex to whomever you are dating!! That's been my experience.

My wife never talks about her ex. He's dead and there's no love lose. We see my children's mother and it's ok ... I think. I see tension in my wife and work with her to help her feel like she's the queen of our castle. I try not to spend to much time talking to my children's mother. I mostly listen to her and her friends journeys. I keep it simple and I'm smart about not doing anything to cause an alert.

Knowing about past relationships and how they describe them can give me valuable insight into their personality and character traits. The information is valuable to me in determining the future of our relationship. Better to know than be surprised.

I went with "Other". The reason is that it depends on the situation, and ALL of those answers have been true for me at some point or another. The way a person talks about their ex, or chooses not to, can reveal a great deal about their relationship skills, and whether they have healed and learned from a previous relationship and what caused them to fail or otherwise come to an end. It could also be educational to listen and learn to avoid mistakes made by their ex. An ending isn't necessarily indicative of failure and could be a sign of maturity.

No problems within normal boundary.

Depends, I would not want to hear about his big manhood and how he used to pound her til the bed broke, but if we are talking within the subject of ex's, it's cool....sometimes people can't stop talking about them, that is a huge turn off.

If im dating someone and they are divorced or just out of a long term relationship, I would want top know why. It might be something like, "They hated it whenever I murdered a hobo," That's important information.

The ex and I were together over 20 years, so it would be impossible not to talk about that phase of my life. I don't rant and rave, and I don't overdo it. I don't know how you could get to know someone new and not talk about your past.

As long as it's relevant.