Getting kicked out of the house, what should I do?

Ok, I'll try to keep this short. My sister, 12, is insultingly stupid and impulsive. And my mom thinks she knows everything about parenting when she can't even control my sister. As bad a parent as she is, I help her to help my sister whenever I can. So I guess you can say, I usually side with my mother. Anyhow, all three of us have been fighting for the past hour or 2 (about my sister being immature) and finally my sister runs off to her room to sleep, my mom follows her into her room (at this point my sister is crying from all the fighting) and my mom continues on to taunt her, calling her a crybaby and making crying noises around her. So I stick up for my sister, regardless of how stupid she is, and I lash out at my mom. I called her a pathetic child and a few choice words. And now she says I have to leave tomorrow, she doesn't care where I go. I feel like it wasn't even worth it, but a 47 yr old making fun of her 12 yr old daughter, I mean wtf? I lost all respect for my mom at that point. Was that the right thing to do?:/