This is beyond disgusting and I hope the girls will get the punishment they deserve, today, tomorrow or in ten years. Besides the fact that they made their fun from humiliating someone and then posting it on youtube for everyone to see, they attacked a younger and smaller person in a group of three. I wonder would either one of those girls try to do something like that to three boys. Of course not, and if they touched her, as many already said, they would be labelled as sexual assailants.
However, the greatest outrage I have is directed to the society which made it "shameful" and "terrible" if the boy gets attacked, if he cries, or if he's humiliated. This is not about feminists or political correctness towards women; it's about the same thing that has been trying to deny women their rights. A chauvinist culture where man is only a man if he is a "true" man that doesn't break, cry, get attacked, get defeated or get tortured, assaulted or raped and so on. Until the society acknowledges that men can be attacked, that they can cry and that there's nothing shameful about admitting your defeat or humiliation and actively searching for justice, this kind of cases are going to be called "pranks". I've read in this very thread things like "If I was the boys father, I would be ashamed" and similar examples of this societal norm that makes it a bigger deal out of the fact that he was "de-manned", that from the fact that this was a fucking assault that shouldn't go unpunished. The poor boy is going to end up being more ashamed of the fact that he couldn't defend himself or such bullshit (as if he could defend himself; he couldn't and there's nothing wrong with it, but the society thinks that's exactly what's wrong), while the whole case will be ignored because, hey, if girls manage to do that to you, you're a pussy anyway, you deserved it, just shrug it off and maybe it hardens you up. As I said, I am disgusted.