I found out this exploit kind of accidentally but anyway, you need to create a death knight and get it to the end of the quest chain where you have to give the letter to Thrall or Varian. Before you read any further, this only works in the zones where the npcs are unfriendly to the Death Knight.
Make sure you have some corpse dust and the Master of Ghouls talent and summon it before you go through the portal. DO NOT complete the quest and you can use the ghoul to attack the npcs in SW or Elwynn. By the way you can mount up now since the new patch 3.0.8. With this, you can trigger the local/world defense channel from whatever you kill and other people will think it's a horde.
I'm not sure if it works on horde side because I'm too lazy to make another dk but I'm sure it'll work in Durotar and Org too. You can't kill some npcs though such as the children and starting area ones.
You can grief other players mainly by killing the auctioneers or bankers assuming that they won't heal them or you can just level up higher without completing the quest and the pet will kill it quicker. Don't worry about the level 75 guards that will spawn because they will stop and just throw fruit/spit at you.
If your ghoul gets low hp then just run out of combat and mount up and it will be at full health again. However, if it dies then just summon it again at a zone where you aren't silenced such as Westfall/Deeprun Tram and Barrens I also suggest getting the Glyph of Raise Dead so you don't have to buy any more corpse dust. I did it by heading to Westfall and flying to IF to buy from the AH and applying it there. Have fun with this!
