first of all you need to be ret for repentance i also suggest you take of your gear also this may only work on PvP servers
In everlook (i guess this works in Tanaris too) you find a player of the other faction doing the "Are We there Yeti?" quest (the one where they have to scare the goblins) the mechanical yeti thats summoned is level 1 and is flagged for the repective faction, you throw a repentence on it, YOU get attacked, the YETI gets attacked and the player who SUMMONED the yeti gets attacked
I've only tried it on a paladin but it may work with other abilities.
Enjoy ^^