Most people have a good understanding of what it means to be a good person. But what about evil?
The scientific study of evil occurs in psychology. The unholy triad of evil of personality disorders are psychopathy, sociopathy and narcissism. These disorders are similar in many ways such that many mistakenly believe they are all names for the same thing. It is vitally important to know how to spot evil people so you can prevent the massive amount of harm they inflict on the world.
With psychopathy the overriding characteristic is the complete lack of a conscience or capacity for empathy. The psychopath is concerned only with himself and will do whatever he can to get what he wants. The Universe revolves around him and others are merely objects of gratification or obstacles to remove.
Sociopathy is a disorder in which a person goes along with the psychopathic behaviors of the group he belongs to.
Deep down a narcissist feels like a complete and utter failure. He deals with this crippling reality by constructing a false reality where he is the most magnificent person walking the Earth.