Earlier today, I was in the Zul'Drak area, doing mah sneaky, sneaky undercover quests for those very unhappy Ebon Blade gents, pretending to be a grunt for another grunt that works as part of the Lich King's recruitment offices from Icecrown.
The particular quest in mind had you controlling Bender from Futurama, after a week of consistent eating and lack of moderation, also known as an Abomination, to gather up Drakkari trolls for slaughter, farting, and proving it's never a good idea to drink pepsi after ingesting Pop Rocks. (Take THAT, Mythbusters!)
Along the way, I happened upon a level 80 priest and mage, both horde. So, the mage, thinking himself a veritable source of jocularity, dragged my mindless slave away and pretty much ruined the quest for me, until I got another.
"Oh, ho ho!" says I, "you wish to play that game, eh?"
So, against my better judgment, I start attacking said mage. However, to my good fortune, his priest friend was holy spec and I laughed off his damage, but couldn't laugh off his healing of my target (Buff Pally DPS). However, the damage had been done. In order for the mage to kill me, which he did, he had to leave his disguise and I, happily skipping on my way, lead them away from their goal.
Regardless of the subsequent deaths on my part, I think my message was pretty much clear.
"I don't have to kill you to make your gameplay experience as miserable as you can make mine. Got that, ya little snot?"
So, to drive my point further into the ground needlessly, I stalked them for about the next half hour and repeated said attacks against the mage or the priest as they tried to complete the quest.
Granted, they got the quest done and I got bored pretending a pair of nerds raging about being griefed by a singler players three levels their junior was getting their panties in a twist. Yes, yes, a level 77 trying to attack two level 80s is a textbook example of idiocy, but hey, that's why we do stupid things, because we're vindictive. Which leads me to the point of this post;
People, regardless of how civil they can be in real life, and even how much they can try on the internet, can turn into M r. Hyde faster than they'll admit.
I use myself as an example.