I had one of my Sims (and might I add, for some reason,an old version of her that didn't look too good) from a previous save get picked by MCCC (as I have it set not to create new townies, but instead draw from my tray) as my Sim's neighbor in this new save (which I'd done to try generational play with aging on); and she was automatically generated with the "Unflirty" trait. I decided to just roll with it, and have her as a romantic interest to my Sim (she was originally created as his coworker) to see what would happen. Let's just say things got interesting.