Relationships: Back Handed Friends

I have multiple friends whom I call "My friends." At least I believe they are. I may have a misconceived notion of what a friend is, so let me spell it out. A friend is someone who is there for you. A friend is someone who will build you up. A friend is someone who loves you. 
Like I said, maybe I have a misconceived notion of friendship, but I don't think a few of my friends are truly my friends. 
I have many friends who will make slighted comments which will send me into a state of tears when I think of it later. These friends have implied I am ugly, I am an overachiever, I'm different, I'm too sensitive, and not any of these in nice ways. 
My friend whom I confide in state that they are Jealous or maybe even just not my friends. 
But they are. I know they are my friends, why do they treat me like garbage?
What makes it worse is that these people claim to serve the same person I do, Christ. They claim they have the Holy Spirit inside them. But why? Why can I see  Christian and a non christian standing side by side talking about the same thing and I don't see a difference. Why do Christians and non-Christians tear people down? Why can I see a kid I thought I respected make negative racist jokes. Am I suppose to stand back and watch you tear other people down? I understand, yes, some people are overly sensitive. Yes, I understand, what you say is in jest. But sometimes when people say one thing they mean another. Maybe that black girl who laughed it off is going to go and cry when she gets home. Maybe she's better at hiding her feelings. You expect me to stand back and watch? 
You say I'm too sensitive? Though that word hurts, as it was meant to be an insult, I will wear that word with pride until you quit acting like the world. I will defend my friends, no matter what you or anyone says. I hate myself every time someone calls me ugly. I hate myself every time someone calls me too sensitive. I hate myself every time I'm told I'm different. I will not stand by while my friends are being subject to this abuse!
So, why do these friends treat us this way? I honestly don't know, and I suspect I never will. I know my response when they treat my friends a way, but I don't know my own response. 
Thanks for listening to my rant.
-Sapphire