Who is the X?

The X is my mean ex-husband, and my loser ex-boyfriend. But "the X" is such a great term because it can be applied to so many people like...my boyfriend's nasty ex-wife (the sole inspiration for this project), my friend's cheating ex-boyfriend, and I can't leave out the barbaric coworker who makes so many of us completely miserable. Landlords, professors, minivan drivers -- so many X'es, so many things to say.