Mean Spirited Sims receive a positive moodlet from being around their enemies. They also receive a very slight mood boost for each enemy they have.
Mean Spirited Sim won't autonomously compliment other Sims unless they have a trait like Schmoozer that allows them to.
Mean Spirited Sims will have a greater chance of winning fights.
Mean Spirited Sims will autonomously use negative social interactions more often than other Sims.
Mean Spirited Sims will occasionally angrily mumble to themselves much like Grumpy Sims if left idle, or even scream in anger for no apparent reason.
Mean spirited Sims are able to troll on forums like evil, grumpy or inappropriate Sims. Then, they may wait for a response from the forum users. Not being responded to on a forum will earn the Sim a negative moodlet.
A Mean Spirited Sim who also has the Good trait has most Mean interactions locked from them, limiting their cruelty factor.
Although many players believe that the Evil trait makes Sims the cruelest, Evil Sims can still have the Friendly trait, making the Evil Sim still polite to other Sims (even without the Friendly trait, Evil Sims are still not particularly bad-mannered in conversation). Mean Spirited Sims, however, enjoy hurting the feelings of other Sims, unless they have the Good trait. However, Evil Sims like it when other Sims experience misfortune, which causes controversy among players about which trait makes the Sim cruelest. Combining the two (Mean Spirited and Evil) will create a spiteful sadist.
Mean Spirited Sims actually get a mood bonus from making or being around enemies.
Mean Spirited Sims have a higher chance of winning fights unless they also have Loser trait.
The "Fight" option under Fight menu will be replaced with "Beat Up".
Mean-Spirited Sims have a high tendency to laugh at Sims experiencing misfortune, unless they also have the Good trait. Mean Sims are still shocked at nearby Sims dying though, unlike Evil Sims who will point and laugh.