I’ve known two definites, a borderline third, and had a relationship with someone I strongly suspect, people with serious missing empathy problems (that’s not just bitterness talking).
Notably, one was one of the most gorgeous girls I know, a tiny wee thing with cascading auburn curls, a sweet smile and huge brown eyes, who went out with a friend and ruined his life by spreading lies and rumours and assaulting him regularly (waiting until, the tenth time she attacked him, this time with a dinner plate, he hit back, to parade her black eye around town). Another one embezzled huge sums of money from a charity I helped found - and used it to pay his rent and have a wild old time. When we finally realised what was going on and confronted him, he merely laughed in everyone’s faces, then threatened our lawyer with physical violence.
All of them were blisteringly charming at first - when I first met her, I dubbed my buddy’s eventual girlfriend “the perfect woman” and said I’d marry her on the spot, and I would have. She ended up stalking another friend of mine for several years.
The embezzler was totally believable and very credible for months. When he “turned”, it was like something out of a movie, and seriously disturbing. I googled him a couple of years ago and found him trying to get funding to search for buried treasure in the Philippines… :rolleyes:
I, being an overly trusting soul, was completely taken in by all of them. Eventually - usually around a year or so - there was a process I now dub as “the cracks beginning to show”, and their true nature revealed itself - at first through inconsistent behaviour and weird emotional reactions, and finally through the unravelling of the tissue of lies they’d told.
Depressingly, I see there is no known treatment. I guess the only thing to do, when you meet someone like this and realise that is their nature, is to run the hell away and remove them from your life - if you can.