I'm 17 and I don't think I was like that 2 years ago but YES. I feel where you are coming from, kids my age are horrible and I think the problem now is that it "sticks" longer too.
Usually someone's a snotfaced brat from 14-16 but nowadays it can start at 12 and carry on until the mid twenties. It's scary.
I know the "typical HS", I'm in HS, and you did an amazing job on her. I wish I could have a cousin like you.
Oh and don't get me started on "emos" my 16 year old sister is in that crowd and she's just like your cousin