Evil little pranks or things to do to get revenge... Any ideas??? ?

my cousin is really getting on my nerves. She is being so squirly, and two faced, 0and its really getting me pissed. She sits there and copy me just to get me mad. When justin bieber first came out she said that he was ugly and couldnt sing. When i mentioned that i liked him, she started acting as if she were his biggest fan. We are at a compitiopn of who could get the most justin bieber stuff, she is a little spoiled brat so she gets everything that she wants. So i end up loosin. She messages my old boyfriends and trys to get with thwm. She turns my friends against me with little lies. She is just being so darn evil. Cause i dont fight my cousins, im too close to her mom and i dont want that relationship to end. I wanna know some evil little shemes like things to damnage her phone, roin her scocial life, makeing people hat her. I remember i put a pair of shitty draws in her school backpack,stuff like that. Give me some evil evil, schemes. And what are some things to absolutely ruoin somebodys goo hair?