Short answer would be: "I'm rubber you're glue, your words bounce off me and stick to you."
But that's easier said that done.
Reasoning again is not to consider yourself with everybody's opinions.

One simple trick I am doing when someone is trying to provoke me. I picked this up from Erik von Markovik (aka Mystery). He is one of the founders of modern Game theory. So, here it is:

When someone tries to provoke you or insult you, blow it out of proportions.

Again, easier said then done. But let us consider the alternatives.
If you ignore the insult, you might be considered "weak" and your social status will decline. Ignoring the insult is OK when your social status is so high that a person insulting you will look like tryhard. (more on social status in separate topic)
Another alternative is to bounce the insult back, but that requires some degree of wit. It will come as you become more social. If not done correctly, it will look as tryhard.
Third alternative (and worst of all) it to start arguing (and become defensive). This is usually what everyone usually does and shows immaturity. Think of one of your friends who is easily insulted. How easygoing is he/she? Do you like being in his/her company? How does the situation looks like when someone tries to make a joke at his/her expense. I bet it is awkward for couple of seconds at least.

My personal favorite (in social situations) is blowing thing out of proportions. It sends the following messages: "I am not insecure by being easily insulted and I like being playful and have no trouble joking at my own expense." It also gives me the right to make a joke at sender's expense. Example: A:"Your nose is huge!", M: "You should have seen it before I did the nose job. OMG, I considered a career as a blood hound. Also I got a discount for the boob job. Btw, I can recommend you to the doctor! He will give you the same discount."

In business situations insults are very unlikely and when they occur you should have an adult approach (ignoring or telling that is not the way to do business).

While joking at one's own expense, newer use self-deprecating humor. It is OK to spin insults to humor but to insult yourself by joking is not OK. Basically self-deprecating humor looks for audience's pity and that is not the message you want to send ("Look at me how sad I am, hahaha").