ANSWER:

You must advise him with good manners, knowledge, diplomacy, and wisdom. If he backbites, you must condemn him or leave his company until he speaks of something else. 

If he backbites people and is bad news, no problem in avoiding him.

I have a friend that has rude behavior towards people even though he has good intentions. Also whenever we hang out he often backbites. I tried hinting at his behavior but he’s a lot older than me and not the type that likes to be corrected. Now I try to avoid him and ignore his calls. Is this permissible? As this is the best solution I can think of.