The only thing you can do about it is stop talking to him. Eventually someone will teach him a lesson about being stupid enough to get on everyone's bad side, or he'll mess with the wrong person. But it's not your responsibility unless you're the one he's messing with. [Roxas doesn't exactly believe in the DF either]
Not everyone can be fixed. Some people... are just lost causes. [and he's not really talking about Helix]