He's the embodiment of slave morality. You can tell that behind his cringey little "you do you!" shit and starting his plebbit comments with "friend, ...", there's real contempt hiding. He speaks this way because he's terrified of confrontation and has no idea how to handle disagreement. It's quite evident that he genuinely thinks he's the shit, but he's just too much of a coward and a mental weakling to face any critique head-on and honourably. That's why he hedges with these weasely little phrases, why he pre-empts all possible criticism with a pre-written and pinned FAQ, and why he saw the need to make that bizarre and incoherent video on why he refuses to use metric conversions.
So it doesn't surprise me that he's prone to the occasional outburst of impotent anger in his comments section from time to time -- he clearly has an ego and a measure of masculine rage, but has never learnt what to do with them, and has spent his life being afraid of any kind of self-affirmation. Why, for example, did he overreact with such vitriol to this relatively benign comment about ceramic stoves? Why does he get so upset over a very gentle quip about the narration? Because that's the kind of language in which Adam would himself codify his criticism. He interprets the slightest of gibes as full-frontal attacks because that's the way he'd make a criticism. Simple, honest and straightforward language is not for him; he lacks the courage to be direct.
As other anons have said, all of this has probably been reinforced/cemented by his having been a professor, where he's been able to go mostly unchallenged in his little fiefdom for years. Now he's suddenly exposed to the internet, where everyone is way harsher, and more importantly, don't need to please him to pass a class. I guess he's struggling to adapt a bit.