1)adj. someone who takes pleasure in the pain of others
2) not to be confused with cruel, some one who is cruel is mean for the sake of being mean a sadist (sadistic person) is someone who is mean for the sake of enjoyment
On a bad day (actually almost everyday) joni is a sadistic witch. (and she is damn proud of that fact)
I am a sadist don't tell me about your problems they only make me laugh harder.