I'd agree that when an insult is untended it may remain an insult even if no none feels insulted. The same can be true when no insult is intended, but someone feels insulted. But I'd draw the line at the situation where no insult is intended, and no insult is experienced.
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I'd say "Hun" was a case of a boast being turned upon the boaster, so that it became an insult, and that's fair enough in principle. I can't see the analogy with "his blood be upon us", which can't be classed as any kind of a boast.