If someone is malevolent, they wish evil on others. If you find yourself approaching someone with a malevolent look in her eye, best to run the other way.
Malevolent comes from the Latin word malevolens, which means "ill-disposed, spiteful"; its opposite is benevolent, which means "wishing good things for others." A malevolent person might display satisfaction at someone else's problems. But it's not only individuals who can be malevolent. If you think that television violence influences viewers to violence, you see television as a malevolent force. The stress is on the second syllable: muh-LEV-uh-lent.
adj wishing or appearing to wish evil to others; arising from intense ill will or hatred
having the nature of or resulting from malice