Interestingly enough, something similar to this happened to me in the original EverQuest waaaaay back in the day. I was playing a Mage and my good friend was playing an Enchanter. We were dueling to pass the time and he had the bright idea to Charm my earth elemental. It of course did not work. It did however apply the ability to the pet. When it wore off, the elemental completely broke free of player control and went berserk on anyone who went near it. It killed 3 Rogues, 2 Bards, 4 Warriors, a Druid, a Shaman, 6 Necromancers, and a Cleric before a high level finally put it down.
Morale of the story: This isn't that far fetched.