I have never been able to see the logic in why this sort of thing is actually carried out.
It is not just mindless vandalism, since has already been posted it could lead to a nasty accident.
I have resorted, in explanation, of these incidents to the words of one of my former pupils. A highly intelligent young man who often carried out vandalism in the Academy. His retort was it is fun at the time!
In my opinion, a pretty sick explanation..