The kid looks like a cheeky little shit (but who am I to judge).
On the other hand, the guy could have just lost his marbles, thought he was seeing gremlins and started lashing out.
I hate it when things like this appear in the news because everyone has their opinion, and thinks it's right, when all they know is what they read in the Guardian or saw on Channel 4 news.
I remember when I was in school, some kids realised pretty early that no matter what they did, nothing bad would happen to them (in their eyes). The worst would be expulsion, then find a new school.
On the other hand, we had a teacher who was (allegedly) suspended twice in my 5 years there, for indecent behaviour towards female pupils. And I once saw him throw a kid against a vending machine because he cheekily replied "George Best" to the question "who do you think you are?" after pushing in the queue.
We'll see what happens...