There's an interesting discussion underway on the Qt3 forums as to whether or not the above video (warning - contains fruity language and crimson epithets!)  is an excusable form of griefing. The video shows a group of players causing no end of trouble to their TF2 team-mates by blocking doors and not letting anyone leave until they answer a trivia question, or by constructing exit portals in front of enemy gun turrets and then enjoying the carnage.

It's admittedly amusing but it's still basically the same sort of look-at-me attention seeking that's often exhibited by the common or garden internet idiot. Art? No, 'fraid not. The ongoing project of Joseph DeLappe is about the only example we can think of where griefing is an excusable - even honourable - pursuit. He gained some notoriety a while ago for logging into America's Army and typing in the names of soldiers who had been killed in Iraq. As far as we can tell, he's still at it, and aims to keep going until the war ends.