I would imagine that this is because NT people fundamentally care about their image: about how the world perceives them. Coming across as rude without managing to be funny at the same time and ending up a social pariah would be agony for someone who cares about that sort of thing. Socialisation is often the only reason they do anything outside of outright obligation, and they want to be loved and appreciated.
I'm not exactly like that myself. I don't go out of my way to be rude but I can certainly be biting and sarcastic when annoyed and just generally blunt. "Yes, your ass does look fat in that and yes your hair looks like you were dragged through multiple hedges full of thorns". But really, I think people should, and some do, appreciate honest observations rather than just hearing the same thing from everyone. Surely that must be dull?
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Power corrupts. Knowledge is power. Study hard. Be evil.