Ix, the direct answer to your first question would have been - to regard it as entertainment, since their chosen means of anonymous communication is the measure of who and what they are. Each to his own.
Yes I'd agree that there are people out there at any time who may be vulnerable to the remarks of others, whether it be over a rotary dial phone or Roman graffiti scrawled on a wall in Pompeii ('Blutus Maximus does sheep'). Its however regrettable that anyone would place any value on an anonymous comment from someone too nervous and bitchy to say it in person. Rather than use the label 'cyber bully' to dissuade or in some way impair the sender's kind thoughts, would it not be better to instead build up and enhance the recipient ?
I certainly agree that exploiting their vulnerability is very distinct to a richly deserved bagging of the more resilient S/O Bloggs because of his selfie doing a one armed bench press, etc.