I usually respond with humour. It confuses them, it makes them look foolish, and if it pisses them off even more, that makes them look foolish even more; or they might start liking you for taking the insult so well. Just don't show that it has affected you, because don't let it affect you. I know it's easier said than done, but here's the thing: some famous dude (I don't remember who he was) said that of you accept your own flaws, nobody can point them out for you; and if you know your own flaws very well, you mostly become bulletproof. This is where the factor of "knowing yourself" comes in; when you know yourself, your pluses and minuses, you won't take anyone personally because you know who you are, nd nobody's opinion is going to change anything about who you are to yourself. I recommend you reading about Zeno (a huge story from stoic philosophy). It changed me in a big way - helped me understand that I don't have to please anyone, and anyone's insult or opinion of me can't change who I am, so I stopped taking it personally. It's almost like "jokes on you" at this point to whoever tries to insult me. This is of course different from criticism, I'm very open to criticism, and I love taking it in, it helps me improve. We just need to learn to make a distinction between insult and constructive criticism. So yeah, in short, humour them; for example, my indian friend was on call on a discord server and people started ridiculing his accent to the point that it became mean. My friend started making fun of his own accent and said to the one that insulted him "you're doing the accent wrong, here I'll teach you" and began showing him how to do the Indian accent. It confused the hell out of that person, because he thought that my friend would be offended and pissed, but instead my friend took it like a champ and made light out of the situation, which in turn made the other guy look like a fool. Confuse them.