Alright, this is a pretty simple exploit I found today when dueling an Alliance. Note that this only works when you duel the opposing faction.
I searched multiple things and didn't find anything that was like this, so please tell me if this is a repost and I'll close it.
Time for the exploit!
1) Duel someone from the opposing faction.
2) Make sure you aren't flagged for PvP.
(It doesn't matter when you do the following step)
3) After the duel begins, flag for PvP.
The character you're dueling won't be able to attack you. You can still attack them, but they can't attack you. I can't really find an important purpose for this right now, other than to just own the person you're dueling.
Have fun ^_^
My friend and I both tested this, and it worked both times. I don't know if it only works for Horde or not. I'm pretty sure it works for both factions, though.
-Tator