@tristanquin,
Yes people express anger in different ways -- however, expressing your anger while damaging someone else's property crosses the line. If you do something so strongly to express your anger where you hurt someone else, yourself or property then your anger crosses the line.
He should be suspended for school for breaking the window and charged for the price of replacing. If he is not punished for this - no consequences - he will continue to be an idiot - he needs how to express his anger in normal ways.
I won't even mention how stupid he is to do something where he has cut up his hand.
The dude has issues.