How do you deal with a passive agressive friend?

My best friend is one of those “saying sarcastic, hateful things is my humor” kinda gal…and I’m all for it in moderation. But everything she says, whether in person or via facebook comment is bitingly hateful to the point of people actually asking me who that bitch on my facebook is. Obviously it’s a defense mechanism of some sort, but damn…how do I squash that sh!# without incurring more hatefulness????