The twist is that I'm polite even on 4chan.
While I disagree with you about Sushigirl, I think you've hit on a real issue in a more general sense; namely, the rise of a kind of 'new sincerity' on the internet that does feel forced and insincere on a fundamental level that goes beyond just us being too irony poisoned. It feels fake because it's often performative, politicised, and selective in nature.
I wouldn't consider Sushigirl an example of this, however. If anything it's typical for smaller imageboards to be polite, in my experience, and Sushichan never struck me as particularly excessive. I think the more valid complaint against Sushichan is that some people take the 'keep it comfy' thing too literally and try to ban things they don't like, but it doesn't really matter as long as the staff continue to ignore them.>>3594
You raise a good point, but in OP's case I really think it just boils down to him misinterpreting the hostility on 4chan. It is or was supposed to be just good-natured ribbing. All of my friends are from 4chan and they are sweet, sensitive souls who just like to shitpost sometimes, but people like OP take everything literally and think they're in good company, when I think the average sushi roll would at least consider OP's deep, visceral hatred unusual. If anything, posters like that are a drag who bring the discussion down with them because of their unresolved personal issues.
I think 'cringe' humor in general has been terrible in the long-run because spontaneous interactions are inevitably embarrassing at times and shouldn't be so over-analysed.