What the fuck is wrong with people?
Complete lack of common sense would be my guess. Unfortunately, this shit can't be satisfyingly avoided before entering the realm of a paranoid rulings and can only be fixed by a proper civic education.
But I don't know what's worse, this kind of things happening in schools far too often or the fact I first knew of this when my youtube "what to see" recommendations dropped this nasty specimen
. (Sorry in advance for linking Fischer.)