I tend to fail a lot:
I fell off the edges in Grim Batol more than once.
On my hunter, I thought you were supposed to Raptor Strike when you stacked.
There was this bug on beta that, if you logged out while mounted in the air, you'd fall to your death upon logging in; I fell to my death as a druid.
If I heal with particle density on ultra, I am distracted by the shinies and everyone almost dies.
My first pvp encounter was when I was a nub: A boomkin was attacking me and I was so amazed by a giant chicken, that I died.
I used to try aggroing owlkin and let them all pile on me, but I was sad that they ran away and didn't know why.
When I first went to Dalaran, I found the elixir in the Underbelly. As a wasp, I tried to 'fly' off of Dalaran.
Before transmog came out, I refused to wear "ugly" armor.
My friend and I spent ten minutes arguing over who would attack the board-guy in Dalaran... he was patched to be unattackable.
I was on my Alliance nub in Hellfire. A level 85 Horde mage had to kill the Fel Reaver about to smush me.
I've fallen off the rocks in Molten Front... a lot.
Speaking of Molten Front, I was carrying my boyfriend on my Nightwing mount. Surprisingly, I fell off the rocks. The druid only caught me.
On beta, I saw Sha of Anger and ran into him.
I've been yelled at for attacking mobs "too close," as melee. Apparently I'm that fail.
I tried to run into Ironforge at level 70 (Horde) to buy a tailoring pattern.
In Tanaris, I tried to aggro those stranded turtles in effort to get them into the water and save them. They evaded back to being stranded.
I drowned because I forgot that my toon was underwater and AFKed.
On Warmaster Blackhorn during my first DS, I somehow got myself trapped in a corner, surrounded by purple stuff. My friends laughed at me.
I walked to Elwynn Forest as a Horde nub.
I forget that CRZ dismounts everyone riding you. Every single day.
As my boyfriend pointed out, I stood in Blade Flurry and died last night.
I play both factions. I saw green Orc names and I was just like, "Whoa, this is bugged. They're friendly!"
That said, I tend to run the path that the opposite faction will.
Honestly, there is so much more than that but I think this is long enough, for now.