Have you thought about just standing up for yourself? Next time she starts hollering at you , walk out of the room. Just get up and leave...lock yourself in the bathroom, tell her to save her breathe, as your well aware of how you suck, you have weight issues and your lazy. Sarcasm at its finest , I had a younger sister who would just agree with my parents when they started in on her... I think it took the sting out and because they didn't get a rise from her they stopped jacking with her... Of course they had plenty of other kids to choose from and they weren't as passive. It takes 2 to interact, so when she starts in... Just leave, walk outside...do the lalalal thing. You could also just tell her to stop, you've heard enough.