to some it might seem strange or weird. i think its a way to express ones emotions and as Dhampy said..its regarded as normal these days for a lot of kids out there. there r plenty of things happening around us for the past several years that would've seemed very strange say 50 years ago. so i guess its a cycle.
It's always been normal. Teens have always been brooding and subject to mood swings and whatnot. It's a side effect of hormones. It's just recently that kids think it only happens to them and whatnot.