Darrell Charm- Hidden evil trait?

do you have MCCC installed? If so, go into console commands and enable Debug cheats. You'll have to restart your game, but then you should be able to shift-click Darrell and look for "Change Sim info" on the pie menu. Click that and then look for "Remove trait". It will come up with a list of traits, both obvious and not so obvious. If he has some sort of hidden evil trait it could possibly be listed there and then you can remove if you so choose to.

The Mean trait does this. It causes a Sim to get a hakppy buff from "joyful meanspiritedness" from saying mean things to other sims, even ones in the same household. And if you had a dollhouse, he'd probably smash it a lot.

Evil sims are different. They get a happiness buff from "being near misery" because in this game, evil is defined as being happy when others are sad, not being happy due to having done something mean, necessarily. They can get the "Near Misery" happiness buff even while crying over an urn, so long as there is at least another Sim there crying, too.

So what you are describing is normal for Mean sims. If you want to remove any Evil, Mean, or Dastardly trait he may have, you can use testingcheats on, then traits.remove_trait Evil (and also try Mean if you want to remove that, and it can't hurt to try Dastardly in case, because that makes them both better at mean interactions, and more likely to choose them.