His mental illness is, he always wants to devalue others
You can't base psychological diagnostics on forum posts. And by calling it "mental illness", you're doing exactly what you accuse him of: devaluing him.
It has nothing to do with psychiatric diagnosis, but it is rather ignorance, because "wanting to devalue others" is not a psychiatric diagnosis.
It is no wonder though since most of the "Lengendary" and "Hero" members here have very low value, both morally and monetarily, and it would be justified for one of the few good members here like JollyGood to point it out. Unless the OP wants to believe that being of "low value" does not exist and thus no one should be "devalued".