I know there are some things which wouldn't be good for a community. Mobbing members might be fun for the rest of the board, but it is noticed from outside and who wants to be the new one in a shark basin? No one, therefore soon there will be only some bored sharks left.
So no, mobbing isn't good, it's evil. But we all know how much fun it is to be evil...
Just for fun, let's assume you wanted to allow your users to be super assholes to each other on your forum: which plugins would you like to have for that?
I could think of the following:
Description: Allow other users (but not the user himself) to change the title of a user. (A history in the profile would be nice)
Description: Each user can suggest an avatar for himself or others. Community can vote which one should be used and the one with the most votes would be the current avatar.
Description: Allows up- and downvoting posts. Increase/Reduce allowed posts per day based on votes.
Description: Allow discussion authors to explicitly disallow some other users to see the content of the discussion.
And it goes without saying that all this plugins come with a popup and mail notification which cannot be switched off
What ideas could you come up with?