Teenagers are absolutely uncontrollable these days (PSA Super Trashy)

My sister, 14 (you should go to jail if you ask for pics) is absolutely uncontrollable. She's been extremely spoiled since birth. My parents (not trashy) can't do anything with her. They are both retired school teachers, Regularly attend church, and my brother and I never had any of these issues. My sister, however, is an absolute psycho. She regularly... like daily.. calls my parents "Motherfrickers, Bitches, counts, etc" it's bad. She's physically abused my mother; hit her, burned her with a curling iron, and threatened her with a knife (super super trashy, I know) My brother and I basically refuse to talk to her and attempt every opportunity to get my parents to seek out a program, meds, psychological evaluation, correctional facility, or something...

Fast forward; All her friends are exactly the same way. I was in the AT&T store the other day, and heard a kid literally say to his dad "I want this phone you fricking piece of shite". What the heck is with kids now days? Do any of your kids act this way?