Trolling...

I think that the pleasure of trolling is the same pleasure that someone gets out of teasing someone in school. He is a bit smarter than your average schoolyard bully, so his teasing and pranks are a bit more extreme, but it is the equivalent of a snotty girl spreading rumors or a bully taking kids lunch money. It is an online version of making yourself feel better by making others feel small, with the results and the intentions being the same, but representing itself as fighting for justice or helping out society.