I research a little bit of psychology and philosophy and learn some details. However, Wikipedia is bit lacking in sadistic topic so I ask here.

What I can know about sadism is take you take pleasure in suffering in others. While it is common among villains, I wonder if it is a normal occurrence for human to feel sadistic because we sometimes encourage the villains suffering and being punished. I admit I am sadistic when I see some deserving villains to suffer.

So is it normal to be sadistic or it is really a personality disorder?