Which means: don't make insults in the first place.
Socially speaking, reacting to an insult gives it credence. If you need to defend yourself, the accusation was vaguely credible; even if it's not strictly true, it's truthy.
Hence, even if it really is true, you shouldn't react to it. Fake it till you make it: act as if they're accusing your hair of being medusa snakes. "No? What?" Act like you don't even understand how it's supposed to be insulting, or politely ignore it the way you politely ignore a faux pas to save the erroneous person the embarrassment.
Given that the correct strategy for dealing with insults is to ignore them, then there's no point in making them in the first place. "Ignore me!" "Okay!" "....wait, I didn't mean it!"
"If you buy a gift for someone and that person does not take it, to whom does the gift belong?"
Of course one must always watch out for irrational or stupid observers. However, by definition, they are weak. You don't want to be their friend, and there's no problem if they're your enemy.
If your audience isn't ignorant, insult reflects only on the person who offers it.
E.g. I always notice it's merchant-caste posturing and I have no interest in merchant-caste games, since they are founded upon falsehood. They're flagrantly disqualifying. "I'm not even trying to speak the truth." "Ah, well, thanks for letting me know. Welcome to my block/ignore/comment deleted list."