It doesn't bother me too much. My main Sim is the big three with Mean, Evil, and Hot Headed, and I think it suits the traits pretty well for her to be mean to even her best friend sometimes. For her friends and family, I never let it dip too far down, anyway.
Heck, sometimes I think the traits don't make her mean enough sometimes. Like when she gets a whim to apologize to someone she's been mean to, especially to someone she's fully in the red with. Doesn't make any sense for a mean/evil Sim to want that.