Yeah, the random meanness is weird. It makes sense for the Mean and maybe Evil traits, but not for Hot-Headed or Erratic. It also shouldn't happen just because a Sim is Angry. If they're Angry, they might react negatively to certain interactions, like Mischief and Romantic, or even Friendly or Funny on rare occasions, but suddenly insulting or yelling at a fellow Sim just because they're in a bad mood doesn't make sense. I might be a bit short with someone when I'm mad about something, but I'm not going to just suddenly chew them out for no reason. Most of us have a bit more self-restraint than that.