If your ex wasn't too "nasty, easy, ugly, fat, dirty, broke, disease-ridden, hoe-ish," etcetera for you to have something with her/him, why does she/he have to be all of that when yall aren't together? Do you think you are like Orbit gum, cleaning it up? If so, check yourself and your ego.
You do not have to disparage one woman/man to interact with another one. Besides, women and men who are secure in themselves want to uplift other women and men. That conversation ripping your ex to shreds is unattractive and ineffective.
It's one thing to divulge pertinent information about an ex or past relationship to your current partner, but you shouldn't lead with denouncement of an ex. It is not an ice breaker. Maybe write down some talking points and step your conversation game up.