Have you had an Ex? I can tell you that is someone with whom a person was once associated, in a relationship, marriage
I have had an ex.  she was crazy!  Have you?
I have had ex friends, It depends on how you define it though because can refer to a variety of different relationships
True.  I was just thinking of an ex girlfriend.  I guess I have a lot of Ex's then.  Ex friends, ex girlfriends, ex employers, etc.
Well, let me tell you now that in social circles and noun is assumed to refer to a former person you have had sexual relations with
That was my initial impression.  I would think that is the most universal term regarding ex's whom people had sexual relations with, right?
People see it as offensive when you start referring to them as your ex. So it's kind of derogatory