(This only works for horde)
A little while back I posted about how to get triple big through use of the grow buff from sen'jin village, an elixir of giant growth, and the BG zerking buff. But I found a way to get the "Grow" buff twice, which makes this a lot easier and last longer.
Just talk to Bom'bay (the "witch doctor in training" in Sen'jin village) until you get the Grow buff and then immediately log off. Log right back on and talk to him again repeatadly until you get the buff again. The two will stack and you'll grow twice. (don't try getting 3, doesn't work). Then take a swig of an Elixir of Giant Growth and enjoy being triple big (you CAN use a Winterfall Firewater instead of the elixir, but it doesn't make you grow quite as big. The two don't stack btw). At that point I usually hearth to Org and watch as people start to gather around me and send me tell after tell of "OMFG" and "HOW DID U DO TAHT!??". It's even more fun when you have some kind of transformation thing like an Orb of Deception or the Ogre Suit from DM North (which I did once, screenshot below), or if you're a Tauren, in which case I'd assume you'd get friggen huge.
One more thing, if you zone into an instance or anything, you'll lose the second Grow buff.
Screens:
http://i71.photobucket.com/albums/i1...2/hugeelf1.jpg
http://i71.photobucket.com/albums/i1...2/hugeelf2.jpg
http://i71.photobucket.com/albums/i1.../hugeogre1.jpg
http://i71.photobucket.com/albums/i1.../hugeogre2.jpg
(I was gonna blur out the names, but then I realized I don't care)
I wanted to try and add the battleground Berserking buff to the mix, but like I said, when you zone into a BG, you lose the second grow buff. I'm thinking it would still be possible to get it, with the use of a warlock and a bit of luck. Not worth the time and effort though.
Anyway, enjoy. This is one of my current favourite things to do in the game.