I worked with a woman who was definitely a psychopath. She presented as a sweet, ditsy, charming person to me, probably because I was useful to her. What was 'off' about her was that she was completely convincing as this person who was very interested in the people around her, but other members of her team who worked with her most closely were openly wary of her, they liked to have communication with her by email rather than conversation so there was a written record. Her charm was actually an information gathering tool, personal and professional info was stored to be used to her advantage in the future. She sucked up to her director, she was very good at finding a weakness and using that to promote closeness, so when anything went wrong she could blame others and the director would be on her side. She operated best on a one-to-one basis and was excellent at dividing to conquer. She would drop little (untrue) comments into a conversation, what someone had said about someone else, that sort of thing.
She would meet adversity with a sort of sweet helplessness, but if that didn't work for her she was scarily and irrationally furious. I did analysis, and I remember a project that she was managing where she had messed up the dates, she came up to see me all quavery and scared and wanting her analysis earlier. In the past I had always done what I could to help her, but this time I wasn't actually getting the data in time, I can't do the analysis before I receive the data. She pleaded and pleaded, and refused to see logic. And then she went ballistic with me, it was scary. Fortunately I sit with a team and my boss asked her to leave. She left spitting nails. Ten mins later her director came storming in demanding to know why I had deliberately and callously made this woman sob by refusing to do my job.
The departments got reshuffled and she ended up with a very no-nonsense and efficient director (a friend of mine) who didn't respond to being buttered up and didn't have any emotional weaknesses to exploit. It all started to unravel quite fast for her then. When stuff went wrong there was a proper debrief to find the issues, so she couldn't just randomly blame others around her. She went to upper management claiming that her new director was bullying her. She took her spite out on junior team members. She took one very bright junior into a meeting room and told her that the director had asked her to have a word with the junior as the junior was being too uppity and speaking out of turn. It was completely untrue, said junior was fantastic at her job and was set for a fast-track and would probably be overtaking psychopath woman in seniority within a couple of years. The junior completely believed her and was desperately upset, but fortunately was brave enough to follow up with the director and so the whole deceit was revealed.
She left because her DH was moving to another country for his work, and after she'd gone loads of stories came out of the woodwork.