I'm starting a campaign with a group of friends, and one player tends to be a bit of a griefer. I'm trying to throw him a bone and also give a controlled environment for this behavior by designing a special bard class for him that debuffs enemies but also hits the party, but it's really important that the party still comes out ahead. We're all in a place where we can actually be emotionally mature about how this goes and lean into the roleplay, so I'm not worried about hard feelings but want to create moments where people realize that he caused them to fail at something.

What's the best way to balance/implement this? I was thinking about having multiple exposures to his performances inoculate the party to their effects, or just have them affect the party at half intensity, but this seems like something you all would have great insight about and I want to get it right.

If it helps, the "performances" are going to be horrible smell auras of different types, like a bad breath effect that makes people fail diplomacy checks because they just want to get away from this dude and will agree to anything unless they pass a will save. I have a lot of crazy ideas but want to keep things a little simple because I've never made a class before.