I'm a ; how do I take criticism?

I'm also Atheist. I used to think I didn't care what anyone else thought of me, but I just realized that I kind of do. Being a and Atheist, it's hard to live somewhere where everyone is a religious Christian redneck bigot (especially if you're a 14-year-old in the eighth grade where everyone LOVES to find things wrong with people and mock them). How do I learn to not care what others think of me? Not just for those two reasons. (/Internet nerd with no life here.) On the internet, I flame a lot of people for whatever reason; for being stupid, etc, and I can rant forever on a lot of subjects. In real life, I get nervous a lot and I can't think of one witty comment for whenever someone says something rude or ignorant to me. How do I make myself not care and be more open minded in real life?