If you really don't give a shit about what someone has to say, then mean it.
2) "Your opinion is irrelevant."
Let a critic know that what they have to say about you has absolutely NO value, then leave the situation. They will try to say something to get under your skin, so don't let them. Don't make a nobody a somebody.
3) Ask your critic: "Why do you think I give a shit about what you have to say?"
Let them answer this question... the results should amuse you. Then, remind them that you don't give a shit.
4) "That's nice."
When someone has something evil to say about your appearances, let them know how ineffective their words were on you by saying "that's nice," then moving on. A bully/critic wants to have an effect on you; that's the only way they can have power over you. When they don't get it, they will move on to their next target.
5) "No, I look like the _____."
When a critic says you look like an idiot/a fool/an ass, say "No, I look like THE idiot/THE fool/THE ass." Critics aren't ever expecting you to have a sense of humor. When you show your sense of humor, it catches them off guard, and completely reduces their effectiveness.
6) "Fuck Off."
Sometimes, you have to put someone in their place. Every now and then, a person needs to be told to shut the fuck up. Do it, and keep it moving. Then, get back to being happy and nappy...
...and stay that way!