I would call taking screenshots (screencapping?) from forum X and posting them on another (forum Y to mock people a violation of the forum X’s CoC. They are definitely making forum X appear “bad”. The Admin or a Mod from forum X should PM both “Bob” and “Dave” and explain what they are doing is harmful to forum X and tell them to stop immediately. They should be told if they continue with their “uncivilized” behavior, they will be banned from form X… no ifs, ands or buts. Forum X does not condone that type of behavior. The hard part of this is they are doing this on another forum. Still, by using posts from the first forum, they are ruining that forum’s name and reputation. That is unacceptable.
Since forum X is “open to the public” - anyone can view and take screenshots of posts - I’m curious as to what is being posted on forum X that can be used in such a derogatory way on the forum Y. Are they twisting words and meanings to suit their hate?
I agree with @HAWK that the owner/Admin of forum Y should be contacted and made aware of these “moderators.” Off-site behavior is awful tough to police. Hopefully, the Admin of forum Y isn’t tolerant of this type of behavior (regardless of the CoC) and will deal with them swiftly. Good luck to you and the users on forum Y.