Psychopaths are prone to sudden changes in personality.
Psychopaths will make you feel like something is wrong with you, due to their behavior. They might at first be the sweetest, most charming person you've ever met and then they have a complete change in personality!
Lack of empathy
They don't understand or share similar feelings, so it's easy for psychopaths to become bullies.
For psychopaths, the truth is irrelevant.
Read the full article on how to identify a psychopath here!