Most people don't put much thought to this trait. Instead, they take overemotional, and that is a good trait, what with increasing all moodlets by 25%. However, mean spirited is better. Let's look at its advantages:
1. Gets a +10 moodlet when near an enemy.
2. Wins fights 40% more often (Except against mean, brave, or evil sims).
3. Has more "mean" interactions.
These don't make it very good, right? However, there is a fourth one (Maybe it should be added to the guide?). Namely, for every single enemy the mean spirited sim has, it gains +5 permanant mood! (Or at least until the enemy sim isn't an enemy, or dies). Making another sim your enemy is quite easy. Merely a rude introduction, then declare nemesis. (A few 100 point wishes or so may appear) This stacks up very quickly. I once made a sim with about 25 enemies. +125 permenant mood boost, all the time. He never had to do anything to help his mood again, Outstanding mood work metrics, etc. What are your thoughts?