Girlfriends sister is a Moran/controling/****?

so my girlfriends sister that is 20yr old think she is the baddest thing ever. Mind you she dropped out of school in 6th grade. She sits at home all day long and do nothing but coupon, take care of the dogs. She has a internet boyfriend, she really doesn't go out unless its to food shop and what not. Point of the story is this how do I get back at this ****. I've so far took her toothbrush and rubbed it on my asshole and pissed in her shampoo bottle. Call me immature or whatever no **** given. But I can not stand someone who can sit home ALL day long while me and my girlfriend both have full time jobs so we can save money to move and have this ***** tell me I don't do anything all day.. when in fact she sits home and mooches off of all of us working people. So if anyone can answer this please help me. I need ways to get back at this dumb ******* ***** so if anyone can help me out her brother, my girlfriend and I would appreciate it.