A sadist is someone who enjoys inflicting pain on others, sometimes in a sexual sense. Sadists like seeing other people hurt.
A sadist is the opposite of a masochist, who enjoys being in pain. A sadist is all about hurting others, usually to get off sexually. However, this word is about more than sex. Anyone who is mean and enjoys it — like a bully — could be considered a sadist. Anyone who tortures another human being is almost certainly a sadist. Unfortunately, we can all be a sadist at certain moments. If you've ever been mean to someone and enjoyed it, you were being a little sadistic.