Why is my sister so mean?

If she is the older sister, then she is mean because she wants to make herself feel superior over you, thinking that she is the best and to make you feel like crap. You are not crap, and try to tell her in a calm matter. If that doesn't work, just ignore her because she's doing everything she can to get a reaction out of you. If she uses other people, for example, and is really nice to them around you just to make you mad, leave the room. My sister is mean too and she always hits me and thinks everything I say is unimportant and how it doesn't matter. Just stand your ground, things will get better!