You're being way too generous. It's common that people who are jerks on the internet seem to be much kinder offline. But it's 2019 and there's no online/offline anymore. If he has a split personality, he requires immediate help. If he does not, he's just a jerk.
Well, anyone can convince me otherwise. Just don't propose http://code-of-conduct.md (or similar) or I'll only put slightly put effort into a counter-argument than the opponent. Which will look ridiculous, and my opponent will point to that. And that's the point. Socratic Method.