Whose fault is it anyway?

It's been a lingering thought throughout my bro and my puberty years - how much of us are shaped by the way our parents brought us up?
Nobody would believe that my brother and I are even related because of the extremity of our worlds, even I doubt myself at times.
He wasn't in such a disastrous state when he was much younger, before our parents were divorced. He wasn't that bad tempered, he swored he hated smoke and would never touch a cig. Look at how much things he said has changed - Club, drink, drive and smoke is the lifestyle now.

They always say that the head of the household are males and that theory has not failed in my house. When my dad left, my brother seemed to naturally take over. Demanding and overbearing, everything has to go his way. My mom is at a loss sometimes she rather remain silent. How did my brother even turn out like that?

Is is really the parents' fault or purely the wrong mix of friends?
I seriously doubt NS will change anything.

Which brother tells his own sister this...
Me: "Can you lower down the volume?" -stereo in the car blasting-
Bro: "You don't like then get out of the car!"
Nothing breaks my heart more than my own family.