Sometimes we do things that we'd rather forget. Sometimes we do those things in a dungeon. My guild has a few funny stories, such as the paladin tank who forgot to turn on Righteous Fury or DPSers who went through entire runs wearing fishing hats.
In my case, I'm ashamed to say that I let a pushy dungeon group get to me and earned my only dungeon finder kick to date. It was late Wrath, in the early days of the dungeon finder when leaving a random still gave you a long, unavoidable DF cooldown. I queued as a healer and popped into heroic Drak'Tharon Keep. I greeted the group with a cheerful "Hi guys!" but was blindsided when one of the DPS replied, "less talking, more healing." We hadn't even pulled yet.
I shut up, but the comment rankled so much that I immediately decided not to heal the DPSer. As a result, he died a couple times throughout the run and was rezzed by the ret pally. They were all from the same guild, so I knew any attempt I made to vote-kick the rude DPSer would fail. I seethed throughout the dungeon, healing only the tank and two of the DPS, and when we reached the last boss, I was the recipient of an unceremonious vote kick. I was angry at the time, but in retrospect, I deserved it. I should have dropped group the moment the comment was made and let them find a new healer. It's all water under the bridge by now, but that's the one dungeon moment of which I'm ashamed.
Have you ever done something in WoW that you wish you hadn't? Was it with friends or strangers? Is it just a funny story now, or do you still feel sheepish?