This is definitely going to catch me some flak, but I'll admit, griefing in online games can be ridiculously fun sometimes. For those not in the know, griefing is intentionally annoying and harassing people in online games, usually by means of teamkilling, spamming, blocking doorways and the like. True story: I was griefing in L4D yesterday, and I managed to aggrivate the guy who made Idiots of Garry's Mod, at least for a while. To me, that's pretty cool.
amount of time spent griefing before kicked x average level of angriness exhibited by others in the game = amount of fun had