Parents. Lack of discipline. Lack of responsibility. Lack of repercussion for bad actions. But above all, when it comes to the internet, remember that there are those people who like to, or try to rather to display their e-noodle and be a big bad tough guy, or an intellectual, etc. Kids are best at imitating what they see, not free or proper thought. That twirp probably saw/heard someone insult the heck out of someone and figured he could do the same.