Invincible Shield In-World, Gamebreaking (Patreon)

The item "Skinny Milk" sold by Kurd Butterhoof in Thunder Totem (39.0, 78.8) in High Mountain has the common "split'n'stack" glitch which allows you to use multiple buffs from the same stackable item simultaneously.  Simply buy as much skinned milk as you can then click on milk in different individual bag slots and you will multiple buffs.

The milk gives you a buff called "Guard". This increases healing effects on your character by 30% and provides you with an absorption shield equal to 10% of your maximum health, for 30 seconds. 

You can theoretically stack your health infinitely: in practice you should be able to stack it high enough that nothing will kill you. 

Does not work in any instanced content.

If you are reading this it means I just posted this...I'm working on a macro to drink multiple milks simultaneously to speed up the process.

EDIT: It seems that a macro to use multiple bag items doesn't exist.  The best shortcut I could find was to make an indiviual macro for each skinned milk slot, eg

cast 0 16

That consumes the skimmed milk in your backpack (bag 0) in the sixteenth slot. 

Then cast 0 15.... etc.

I'd then click on the up arrow on the right of my bottom action bar and fill in all the empty slots with these milk macros. 

So, then I can just click up on the right-hand side of my action bar and quickly press keys 1-10 (or whatever you bind those keys to). A very ugly solution and I'd appreciate alternative suggestions, but much better than clicking on your bag items.

EDIT EDIT: See Spencer's comments below-apparently you can just take each individual milk and put it on your action bars. I'm having difficulty with that for some reason.

EDIT EDIT EDIT: See also Doug Timbs comment: the add-on rotacast apparently automates the procedure.

Sunday 21 May update: This has been posted twice now to bug report and there are indications a LOT of people are using it. I held off on this one because you guys seemed to like this one but I'm making a youtube video of it now since the cat is very much out of the bag.