One time, back in 2005, I fell asleep before a Majordomo Executus pull in the Molten Core. I conked right out seconds after the pull. This probably wouldn't have been a huge deal if I wasn't a main healer. This incident was probably the most embarrassing thing I've ever done in WoW, and I still am reminded of this fact every once in a while. Well ... maybe not the most embarrassing, but definitely up there. Like that one time I was tanking Malygos and my sword broke, leaving me to hold aggro with a shield, Consecration and Hand of Salvation. I didn't hear the end of that one for awhile. Or that time my mouse auto run got stuck and I ran right into Vaelastrasz, wiping the raid. Or that other time when I forgot to equip my Phaseshift Bulwark ... you can imagine the result.
I guess what I am trying to get at is that I've had my fair share of screw-ups. Nothing devastating, but screw-ups none the less that stick with me, haunt me and never let me forget that I am still a human being, as opposed to the invincible tank I like to pretend I am. My mistakes were never handled maliciously, unlike the torrent of hate that has been exemplary of pickup groups. Mistakes are mistakes -- one won't kill you. But you may look like a doofus.
Now, it's your turn. You've made mistakes. We all have. It's confession time. What's the biggest screw-up you've ever been a part of during a group or raid? What was the reaction?