Can we deactivate this festering emotions ?

You might be able to Apologize to reduce the sentiment duration (not that you should have to!) Otherwise you have to just wait for it to go away, and avoid Wolfgang in the meantime as best you can. If you look at the Festering Grudge sentiment in the profile for Wolfgang, you'll be able to see the timer in there -- how filled-up with red the circle is -- it empties out bit by bit and then it disappears.

Thank you @mightysprite for all your advice ;) Its really a pitty we can't toggle them on or off in the game options. I especially don't like them when I play my 100 baby challenge and siblings don't like each other's company. Makes for uncomfortable gameplay moments.

Bullying should always be a no no & should never, ever be in a game. :s
However that being said, is your Wolfgang sim suffering from the fury, cause it's a side effect to being a Werewolf. They're not supposed to be around other sims when that happens.

I agree, my sim instead started being kind and then all of a sudden he became her crush and now they are off to the prom together :o But yeah not sure if that will stop him bullying other kids though, was a little disappointed when I saw him going around fighting everyone and anyone in school.

Well they do nerf everything so a mean sim needs to be mean, if you take away that trait though they do chill out, I have noticed that it wears off, faster now since my girl got closer to him on social bunny and generally hangs around her other friends. The other one that just followed her group let up after a day and the sentiment comes up around them but he doesn't interact with them on his own I think there is supposed to be a cheat to remove sentiments but they probably need to be updated to work with the new pack I don't know for sure though so you may need to look away.

Nice to see they are allowing a few real-life-like negative experiences into the game now. Some of us were finding it a bit too soft and fluffy

A one way trip to a pool with a wall might be the "easiest" way to work around the whole mean Sim issues.

Can't beat them verbally, beat them with the enticing pool offer.