How come my best friend is allowed to b*tch at me, but whenever I"M in a bad mood, she throws it in my face?

Seriously. I love her to death, but shes in a b*tchy mood EVERY morning, and pretty much every day. I just ignore her because I just don't want to have anything to do with her. But how come whenever I happen to be in a bad mood, or act slightly b*tchy to her (even if I'm not being a jerk, which frustrates me) she throws it in my face and says stuff like "um, chill Kate." or "jeeshhh, someones in a bad mooood." like all sarcastically so I just want to rip her head off! Then of course whenever I say I'm not in a bad mood and I'm not being b*tchy at all, shes goes like "Oh, ok, ok.. . yeah I see. Ok ok." In this obnoxiously jerky sarcastic voice that I can't possibly explain. I seriously don't know what to say! Ergh.