Don't bring up past relationships, especially for no necessary reason! If the first thing a woman tells me on a first date is about another man she was romantically interested in, at best it shows she's still thinking about that person, even if only to tell a joke. At the worst, it tells me they're still hung up on that person, and I'd be little other than an attempt to fill the hole that other person left. And I will admit for myself at least, it can also make you jealous further on in the relationship, so maybe it's just a general rule throughout!
Maybe I'm just an easily jealous person aha, that's pretty likely too