Hail Seitan! --> many vegans (including myself) swear on pure gluten :D

And yes, I also know people who also cannot be vegan because of all their dietary restrictions.

I guess the similarity of arch users and vegans lies in the fact that both groups are very much outside the norm. So you often have to distance yourself from the assumed default (windows/apple computer, omnivore diet). And just talking with other people, it comes up often by itself. If someone asks me to fix their windows PC, I have to tell them that I haven't really used windows for nearly a decade now. And if someone invites me over or to a restaurant, I have to tell them that I'm vegan. But people who are inside the norm often don't deal very well with outsiders, so they have to invent tropes like the annoying vegan. What is actually annoying them is their own double standard they have to live with (torturing/killing animals and having a large ecological impact vs wanting to be a good human being).

But obviously there are also some people who use arch or are vegan and do it to provoke a reaction, to feel special and morally superior.