Is it possible all teenagers act selfish and grownup because of bandwagon?

I don't know but from listening to conversations my brother has and some of the things he says i believe most of teenage behavior is bandwagon appeal. I think they act the way they do because all their friends act that way. They also have this notion that if you're a teen, than you're "supposed" to be disrespectful to parents etc. It's like they think we owe them the excuse that oh they're just teens so let me step back and let you just act like a grown thirty year old man.