this gave me the idea for the title/question.i love those do or die moments, when you instinctly do something during some wild battle that succedes. Its the best feeling ever. Like during the Mount Hyjal fight (not the last one, but the one before that), when carol died after she put a sheep on one of the evil locks (or whatnot). She was on vent "Circle is breaking in 5 sec..." desperately warning us that this is bad, and I ran up there put a trap down and dps'd on the other baddies while i could hear Carol on vent going "Awesome Pingu!". That was a nice feeling. And thats what I play for. Im on sure you have had a ton of those moments yourself. Love 'em, couse those are what this game is all about.
here's some of mine:
kintoll: taking down the last 10%(ish) of aran on my own while getting healed by oikid in his pvp set. i was hammering on my keys like a madman to let my spells go as fast as poss
vaelthas: first time i practically solo-tanked karazhan. tbh, any occasion of taking on 4 or more elites at the same time and keeping em on me feels leet
sending out all my love to the healers after that (providing they don't let me die