" Young divided undergraduates into "stains" and "socialites". Stains were the "small, vaguely deformed" breed, replete with acne and anoraks, who had not been to schools such as Eton and Westminster, and who "scuttled across quads as if they had mobile homes on their backs"."
It is not clear from this paragraph, but in the book it is clear that TY is claiming 'stains' as a genuine term rather than one he has made up.
Now let us mock, more in derision than in irk:
""Anything with the word Oxford in it is a sure-fire loser," Young tells me now. "When my friends send me their memoirs, I tell them to remove all references to Oxford because, otherwise, the papers give them to reviewers who went to second-rate universities, and you get the same chippy reaction. Anyway, we were a bunch of insufferable, jumped-up prats who deserved criticism.""