My sister hates me. All she ever does is pick on me and argue with me. She even threatens to steal my stuff. She always says she's the favorite child. She calls me names. I never did anything to her! She's just such a bitch and I wanna slap her?

Wow YOU sound like the b*tch to me! You wanna slap her really!?!? You know what, I would DO anything to hug my sisters again just one more time! How are you gonna feel if you wake up one day and God forbid your sister is dead! And don't say it will never happen because it DOES! Now go give her a hug and tell her you love her! I bet you anything your being nice will CHANGE the dynamics of the relationship!

Welcome to sibling rivalry in the teen years. Just ignore her and move on. Eventually you will work everything out and become good friends.

Just tell her this:

"Well, if you WERE the favorite child, you wouldn't feel the need to threaten me.  So you must think *I* am the favorite child, and feel jealous and resentful.  I'm sorry you feel that way.  But don't worry.  I love you as only a sister can, and you'll always be special to me."

Then just walk away.

Don't get pulled in to it or you are letting her control you and why should she have the power to upset you? Buy a lock for your bedroom door, or wardrobe. I had the same problems with mine, I really didn't like her at all, and although we got on a lot better as adults and when she had children, she hasn't really changed, she is still a liar and incredibly manipulative, but believe me, it catches up with them eventually.

Why don't you talk to your parents about this.  Not sure how old you are, but I'm sure they're aware of the problems between the two of you. They should help to mediate this.  Keep in mind though .. It sounds like your sister might be a bit threatened by you if she tells you all of that.  She might just think you're the favorite ... Sounds that way to me.