Your sim doesn't have to be mean to be genuinely evil.
Never forget that it's not only about what trait you have, it's also about what others have.
Case in point - Bella goth has flirty trait and thus she has no issue making her spouse jealous and see nothing wrong with it. In my current game, she cheated on Mortimer, divorced him, remarried, cheated on that guy and got divorced again (praise MCCC).
All because she is a flirt, all because it's way easier to get her to bed (praise certain adult-only mods). I know - mods, but still.
Evil trait makes sims cartoonish. Caricature, a parody IMHO.