Found this out by accident a moment or two ago, might be basic knowledge but I'm pretty sure some dont think about it.
Had just had a rogue attack me repeatedly so had my pet on aggressive, then I hs'ed to a alliance&horde base without remembering it. My ghoul immidiatly pounced a hunters pet, which fought back. Thus when the guards had killed both pets they came for us owners, I was already half way out of town by then of course so only the poor nelf got guardwhacked but still. I know its game mechanics but not many have their pets on passive in towns it seems. Might be a amusive way to grief. Hit the pets or the owner so that their pets attack you. Then leggit.
1. Be in Town. (A base for both alliance and horde with Guardzone)
2. Attack person with pet or the person pet.
3. Hope that enemy pet isn't on passive.
4. Watch guards come for you and the pet.
5. Get the hell out of there and watch pet owner die.