contact BlIZZARD and file a report
sounds like a lot of fun for that guy
There is only one god and his name is Sargeras.
It does sound like your the only one reporting him. You need to get everyone in the raid to report him. The more the merrier.
Here is my 2 cents in the meantime and please take into account I have never tried him so feel free to laugh and poke fun at my suggestion. Everyone buffs up in a location that's far away. Once everyone is ready make "3 teams". Team 1 consists of a Tank and Healer and Team 2 consists of Tank and Healer. Team 3 consists of everyone else.
Team 1 approaches from one side and Team 2 approaches for the opposite side. Griefer goes into action and kills one of the Teams while the other team moves a bit farther away. Griefer should die and at that point the "alive" team grabs aggro while Team 3 charges in. The dead team should be able to rez and rejoin the fight before the boss is dead. If the boss can't be taunted then the griefer shouldn't be able to do anything while the fight is going on.
Have no idea if that would work but only one way to find out.