There’s a quest named “The Totem of Kar’desh” where you escort a captive out of Sunspring Post in Nagrand. There’s an Alliance and Horde version of this quest. On PvE servers, the game allows you to kill this NPC without flagging you for PvP, thereby allowing you to grief the other faction on this escort without any repercussions.
There were a couple of Horde players who continued to do this at Sunspring Post–every time players would wait for the NPC to respawn, there would be a Mage who just waited for the NPC to get near the exit before killing him.
That must have been changed recently. I remember specifically (back in Vanilla) that Horde escort from Northwatch Keep could be griefed by Alliance players, but Blizzard disallowed that in WoW Classic and changed the way the NPC works.