Biggest Dating Turn Off: Talking about your ex (wife or girlfriend) or current dating life while on a date with someone else
Even if you’re not interested in someone it’s unkind to talk about past or current romantic or dating relationships while on a date with them. If both of you are equally interested in talking about it, proceed with caution. In general it’s best not to.

I once met a man for lunch who talked about his ex-wife and his attorney the whole time. I still regret not politely ending the date. Whenever I see him I remember. I feel sorry for other women he dates until he changes and becomes less wrapped up in his ex-wife and his self.
I have 2 end goals in mind with first dates: learn something new (about their profession, life, and about them) or to have fun. Remember you might run into this person again in a different setting (like in a professional environment). If I hit one or both of these goals the date is a success.

TIP: Focus on the person you’re with (even if you determine you’re not up for a 2nd date). Show kindness. If you do date longer you’ll get plenty of time to dwelve into each other’s pasts. In the beginning stick to safer, more general subjects.