Creating Realistic YA Characters: Understanding The Teenage Worldview

One of my frequent complaints about some YA novels is that the teenage characters don't act/think like real kids.  Numerous authors forget the painful and embarrassing truths about puberty and what follows for the next few years.  Let me remind you and illustrate for you how 7th graders think.
Rule #1: Teenagers are the most narcissistic beings on earth, even more so than the average celebrity.

Illustration #1:  Just before the beginning of my 7th grade year, my mother had to take me shopping to get my required gym suit (a horrible, polyester, one-piece affair).  She picked me up from dance class -- and I had to go to the mall wearing a pair of denim shorts over a black leotard and pink tights.  I remember my humiliation, my fear that everyone was laughing at me as they passed, how every single person in that busy mall would think I had no fashion sense whatsoever because I was wearing shorts OVER MY TIGHTS!  Oh!  The Horror!!!!!
The experience was so dramatic that I can still feel myself cringing in that 12-year-old shell, even as I chuckle at it now.

Illustration #2:  A conversation between a 7th grade BOY and me.
Boy: I'm cold!
Me: You're only wearing a tee shirt.  Don't you have a hoodie you could wear to school?
Boy: Yeah, but putting it on would mess up my hair.
Me (rummaging in my desk for something I don't need in order to hide my smirk): Well, you could put the hoodie on BEFORE you gelled your hair in the mornings.
Boy: But then if I got to warm during the day, I'd have to take the hoodie off, and that'd mess up my hair!!
Me: What about getting one of those zip hoodies?
Boy: I got one for my birthday, but I don't wanna mess it up yet by wearing it to school.

Ah, doesn't your heart just bleed over his dilemma?

These realities, folks, are the ones that drive YA characters.  Narcissism is just one element, but it has to be there, or the fictional characters fall flat.
Sometimes adults ask me how I "dream up" all the hilarious situations that Eric (of Half-Vampire fame) gets himself into.  But kids never ask me that; they know Eric seems real because he acts just like a real kid.  To create the awkward and humorous situations, I simply write characters that react like a real teenager would.
Nerissa MacKay of my WIP which is in the "resting and ripening" stage is delightful in her narcissism. She, like so many teenagers, desperately wants to be SEEN, to be important, to have groupies, to be a star.  She tries so very hard to stand out and be "above" the ordinary.  And that is why I just had to have her accidentally turn herself invisible.  What could be worse for her than to be completely unseen?  Ah, adolescence!   There is a reason why most of us would never go back if given the chance.