Friend going crazy and misrepresenting me online?

Just act like it never happened. Keep talking to him and say "we got off on the wrong foot, I think we both misinterpreted something, let's start over". You would want to keep him on your good side instead of your bad side. Now you know what he is capable of so keep him at an arms distance. stay nice to him and don't try to comment on any negative things he brings up.