In Terrace of Endless Spring, one of the mobs in the first boss encounter (Asani), will use a spell on a couple random players called Lightning Prison Spirit Link Totem - Spell - World of Warcraft. . If you leave the instance while Lightning Prison is on you, it will not be removed.
1: Queue up for ToES LFR.
2: Engage 1'st boss.
3: As soon as you get Lightning Prison on you (not the stun, but the pre-stun debuff), leave the group.
4: You will get back to wherever you were before you queued up.
5: Stand on top of another player and watch as their health slowly goes away.
This is of course optimal if you are 2 people doing it, seeing as 1 Lightning Prison won't be enough to kill a geared player.
Also, you will be stunned while it is on, so you can't chase people. (You might die, so having a CD or HoT's is optimal)
The faster your computer is, the more optimal the exploit will be, since you will have a slower duration left on the effect when you get out of the loading screen if your computer is slow.
Pro tip: The damage does not spread on multiple targets, so for optimal murdering, use it in the Orgrimmar Auction House.
Note: It's important that you leave before you get the actual stun from Lightning Prison. I'll post a screen-shot of it later.