Gamasutra have a quite in-depth article about Online Gaming Idiocy and how to fix it, psychological style.
[In this in-depth article, Fulton discusses why "the online behavior of our customers is dramatically reducing our sales", referencing his social design on Microsoft's Shadowrun to explain how we can dissuade anonymous Internet gamers.
Warning: This article uses language inappropriate for a professional website. Unfortunately, the language used is far less offensive than what is commonly encountered in online gaming.]
Some gamers are fuckwads
Of all the ways I spend my free time, playing games online is the only one I would describe as "frequently barbaric". Insults of all kinds, including racist and homophobic slurs, are commonplace.
The women I know who play online avoid anything that would identify them as female -- including voice communication -- in order to avoid the unwanted, and frequently negative, attention.
And that's just how players are intentionally insulting -- what some people do while playing online can also be aggravating.
Cheating, team-killing, entering a game but not playing, quitting before the game is over, and more, are all relatively common. Common enough that it was deemed worthy of a Penny Arcade comic, speculating about why normal people become fuckwads online.