I have met a group of 5 Allies escorting him once, they noticed me and since they know how horde can be there in such situation I could already see the fear in their eyes.
I followed them using emote like /evil and so on... they started using emotes like /beg /no, the terror they felt for that long minute was palpable.
Few seconds before the end, being able to one-shot him, I started the long casting of SoulFire... but I interrupted it.
I was already satisfied of the psychological terror I gave them.