While on the quest, A Tangled Skein, the player is sent to use a web gun and bring down Plague Sprayers near Kolramas in Zul'Drak. Strangely enough, the Plague Sprayers are attackable. If you attack a Plague Sprayer, you tap the target. Where the glitch comes in is that these Plague Sprayers stay tapped to you until they die, no matter how far away you are, alive or dead. While tapped, a player is unable to shoot down the Plague Sprayer from the sky, so, if someone has all of them tapped, you can't complete the quest.
So, in order to grief both Alliance and Horde, shoot every plague sprayer in the area south of Kolramas, then run away. The next person trying to do the quest will have to kill every Plague Sprayer, wait for the respawn, then shoot them down with the gun.
Enjoy being jerks! =)