I don't want to spoil the 'woo evil' party, and I definitely have had a sense of badness off someone or really disliked them for no reason, but..
Some of the symptoms people are describing in others relate to mental illness. I've seen a relative get those 'black eyes' which really do seem possessed, actually they were having a psychotic episode and once that had passed, their eyes have been normal ever since. I've also seen the black eyes on someone else with a severe mental illness, in his case he was violent during that, I have no idea if he is cured.
Those saying about the baby eyes, I think these type of thoughts about your child being evil are extremely common not just with PND but the psychological disturbance that comes after birth, pregnancy-related psychosis, which may not be full on, also stress/exhaustion/hormones. I know I was utterly mad the few days after birth and believed I would die, didn't see the eyes thing, but it would not be atypical and certainly isn't anything to do with the actual child- it's your own emotional/psychological disturbance.
Blank emotionless faces, yes, it could be linked to being a psychopath, but a relative of mine has epilepsy and these blank faced episodes are really disturbing, it's like you lose them and they almost aren't there at the time, but it's hardly their fault!
True psychopaths are often charming and socially skilled, hence the danger, as in fact, they don't alert the spidey senses.
I'm not dismissing all the episodes here at all, and I do believe in following your intuition and getting out of the way of people that make you feel bad, unsettled and so on. But some of the things people are talking about are really connected with neurological disturbance, illness and so forth which make the brain unable to allow the person to behave in a way we find normal, and there is a long history of miscarriages of justice based on the fact people do bizarre things (confess to things they didn't do) or seem bizarre (are mentally ill or socially isolated), but people 'just knew' they did it.