When I was a teenager, I was especially angsty. I was always getting into trouble or getting into fights with my Mom, it got to a point where I was grounded practically all the time. Looking back, I don't know what I was so angry about exactly. I was given everything I wanted, but I guess I always wanted more- brat!
I was telling a co-worker about it yesterday, and she said that she experienced the same thing. She hated the world, and the world hated her. Teenage angst is quite common, thanks to a bunch of raging hormones, pressure from school and parents and most importantly, peer pressure. You have this new body you aren't used to (hello, puberty) and thanks to popular culture, if you aren't wearing the latest, you'll probably be laughed at. That desperate need to fit in is definitely an issue for most teenagers, causing anxiety and sometimes even depression.
When dealing with a teenager, take all these things into consideration and keep your cool. Be patient. Remember, you were a teenager once too.