I think we now have a society were many children have never been "told off" and they can almost do what they like.
So when they ARE told off, they react like this.
Some schools seem to be scared to tell kids off so behaviour in some schools is terrible, and kids get away with it.
Some kids grow up demanding laptops, smartphones, games consoles, TVs in their room etc. and many parents just give in and give them what they want, so the kids are never told NO.
We also have to realise that the behaviour of some of these kids parents is also bad, so the kids grow up believing that bad behaviour is OK, and if anyone complains then you beat them up.
I also believe that society is far more "angry" than it used to be (re the question you posted earlier about the fight in the ASDA car park).
Anger seems just below the surface in many people and it takes very little to being it to the surface. Even "giving someone a funny look" sometimes seems an excuse to stab someone to death.
If you look at film from say the 1950s people seem much more relaxed and happy and easy going, and it would take much more to bring anger to the surface at that time.
I am not saying there was not anger or fights in those days, just rarer and probably only amongst a smaller "set" of society.