[SzczerbiakManiac]

Wired UK has an article readers of this thread may find interesting.
Online disinhibition and the psychology of trolling

Here's just a small portion:

Common wisdom dictates that people are more aggressive, rude and forthright online because they're anonymous and can act as unpleasantly as they like without immediate consequence. If you're irritating in real life you risk at best social sanctions and at worst a physical assault. There's definitely evidence that points to anonymity as a factor, especially in the internet's early years when IRC, Usenet and message boards were the norm, but nowadays Facebook commenting has added a personal touch, seemingly without significantly curbing the aggression.

Psychologist John Suller wrote a paper on this in 2004, entitled "The Online Disinhibition Effect", where he explored six factors that could combine to change people's behaviour online. These are dissociative anonymity ("my actions can't be attributed to my person"); invisibility ("nobody can tell what I look like, or judge my tone"); asynchronicity ("my actions do not occur in real-time"); solipsistic Introjection ("I can't see these people, I have to guess at who they are and their intent"); dissociative imagination ("this is not the real world, these are not real people"); and minimising authority ("there are no authority figures here, I can act freely"). The combination of any number of these leads to people behaving in ways they wouldn't when away from the screen, often positively -- being more open, or honest -- but sometimes negatively, abusing their fellow internet users in ways they wouldn't dream of offline.

Internet psychologist Graham Jones believes that to a certain extent the kind of aggressive behaviour often seen online happens in the real world. "Having said that, there is a feature of the online world that makes such negative behaviour more likely than in the real world," he says. "In the real world people subconsciously monitor the behaviour of others around them and adapt their own behaviour accordingly... Online we do not have such feedback mechanisms."