Yes, I've met a couple of people who I thought were downright evil, as in if they had a choice between hurting someone and not hurting someone, they would simply take the choice that benefitted themelves the most without caring. Or in fact take the choice that caused the hurt, because they enjoyed watching someone else suffer.
But I tend to weigh up evidence, and observe, to see signs. One person I knew very well, knew his family (absolutely lovely), but I always had doubts about him and the way he reacted to things/behaved. I ended up in a relationship with him before he ended it very callously. It became obvious when he did so that there was something very very wrong with him (I won't go into detail but it went well beyond the normal ending of a relationship).
You would literally catch him before he had managed to compose his features and there would sometimes be this evil expression on his face. But he's behaved badly to a lot of people, not just me, and has no contact with any of them now. He can't even hold down a job and lives off his parents. But my gut instinct had always been telling me this about him, although I obviously had to find out for myself. The strangest thing is, he's very attractive and comes across as very gentle and kind, and sort of shy, so its the sheer change in him from that to being callous which isn't that hard to spot at all. But many people think he's angelic.
One of his past exes also committed suicide within 6 months of him ending it with her.
I then did a little digging and found out that his grandfather had done something really bad and was actually quite notorious and I saw a photo of the grandfather online, and there was just something chilling about the way he stared boldly into the camera.
Once when I was showing a woman round my house when I had a room for rent, I had a sudden flash of insight and I just knew she was evil. Well, she asked me for a glass of water just as she was leaving, and there was something so calculated about it, as if she was assessing me to see how easily I could be controlled. So I ushered her out as quickly as I could after giving the glass of water and told her the room had been taken by someone else.