Er, exactly my point, actually—the only example I could even find of a derogatory exonym used by “barbarians” was just the equivalent of “barbarian.” Not, as Amateur Barbarian put it, the Viking version of “pot-pooping poof.” (Pottinn-skítapúffingr?) Hence the problem.
While “civilized” societies would call the rampaging hoards “barbarians” I doubt that the “barbarians” thought of themselves as such. :mad:
They would have considered themselves the superior/better society and probably referred to anyone else as “barbarians”
So at a guess I would say terms like “barbarian” and the like worked both ways 
Not necessarily. The Biblical tribes that the Hebrews often antagonize are generally called (by the Hebrews) “the Somethingites” or “the Somethingim”, where Something can be the place they come from, or the name of their head honcho, or possibly a remarkable feature/specialty of that particular tribe.
For example, there’s debate on whether the Kenites were a) the people of Cain b) The Blacksmiths or c) The Spearmen, but none of those exonyms are particularly derogative.
Not a noun, but I imagine words like “decadent”, “effete” and “soft” would be the sorts of words the “barbarians” used to impugn any civilised nations they didn’t like.
The Gaelic word “Sassenach”, meaning basically “someone who’s not a gael” comes pretty close, considering most of the people who weren’t gaels eventually became more “civilised” - in tems of technical advancement at any rate
From what I read it wasn’t so much derogatory as descriptive, although I suppose that’s derogatory in the sense that it shows a lack of care for what the people so described called themselves. The wikipedia article links the etymology to the inuit wearing animal skins rather than wool clothing.
Massholes?
“Hujaa” is a racist, derogatory Mongolian word for the Chinese.
Whether the word was used already back in Ghingis’ day, I do not know.