I'd say the adolescent stage in life is the most complex of them all.
It's the point in which our bodies require the most amount of nutrients/energy, and reasonably so, we're growing at such a rate and developing in so many ways, that it's vital for our bodies to constantly stay fueled.
Copious amounts of hormonal changes/imbalances also take place, and it's bound to trigger a plethora of emotional conflict, even with the adolescent alone.
Being one myself, it's almost as if we're more susceptible to stress, it's just a matter of how it's coped with. Think about it, you don't hear about many adults dealing with stress via cutting themselves, then get these 14-17 year-olds slicing their arms with razors as if they're using their bodies as a make shift Etch A Sketch. It's a morbid image, yeah, but that's how it is.
I don't even know what I'm talking about though, but yeah, some adolescents can be annoyingly egotistical, from my experiences at least.