Someone who is malicious enjoys hurting or embarrassing others. If you're writing a book about good and evil, you'll want to come up with a truly malicious character to do all the bad stuff.
Malicious is the adjective based on the noun malice, which means the desire to harm others. Both words come from the Latin word malus, for bad. If someone is malicious he doesn't just make bad things happen; he loves to make bad things happen.
adj having the nature of or resulting from malice
despiteful, spiteful, vindictive
showing malicious ill will and a desire to hurt; motivated by spite
showing sly or knowing malice in a glance
wishing or appearing to wish evil to others; arising from intense ill will or hatred
having eyes that gleam with malice
bitchy, cattish, catty
marked by or arising from malice
poisonous, venomous, vicious
marked by deep ill will; deliberately harmful
full of malice or hate
shrewish and malicious
not malicious or spiteful