psychopath -Brian-

Psychopathy is a psychological construct that describes chronic immoral and antisocial behavior.

http://wiki.answers.com/Q/How_can_you_tell_if_someone_is_a_psychopath

If you go upside website you can check how can you tell if someone is a psychopath.

In Korea, there is a drama named 'Story of men.' At there, a man named 'Chae Jungwu' is a psychopath. He enjoys very cruel things. For instance, when he was young, he watched a bird's eye which he picked out, and he broke a bird's legs and tore its wings. Also, he smiled seeing his mother who is dying because he gave her drug that make kill herself. He is not a person. It's so atrocious.