How to make my sister stop being mean?

My sister is always constantly teasing me and my mom and dad don't care! She came in my mom and dads room which is where her xbox headset was and she took it and said "loser" when i did nothing! Then she took my ipod and went on it and looked at a video [it wasnt bad just me making a sundae LOL] and she went in the bathroom, locked the door and watched it! It gets really annoying how she thinks she is the boss of me. She uses me also! Like I'm her maid she asks me to make her stuff and I say "ok" so nothing bad will happen! I feel like I'm a slave :( She does alot of mean stuff to me and I'm SICK of it! Thanks.