I can't stand my friend anymore?

Except for a couple of awesome friends, I'm not that lucky with my friends. My one friend who I hang out with every day, is either nice one day, or a total jerk the next. I carpool with her to go to school, so really I can't avoid her. We were instant buddies since 5th grade. But since a little bit ago, she's been trying to act older than she is or something. She's always calling me cuss words. She thinks of every name and the book and then laughs about it. I call her names back but I honestly don't think it's that funny. Today she was pushing me off the sidewalk when we were walking to this place where we sit down at to wait for my mom. I pushed her back and then it just ended up it this whole pushing fest. She's really getting on my nerves. She's always bragging about her life, or telling me how her life sucks. She never really cares about what I say unless someone died or something. I know I can't leave her though, because every once in a while we have fun, and that would be just super weird with out her. I have this other really good friend who is true and awesome, but I can't sit by her at lunch because I have to sit by my other friend. My other friend has other friends too, but we basically stick together. I'm just tired of her though, and her actions. We're still friends, and I'm hoping soon I'll regret creating this question. What should I do?