Mine, predictably enough, took place on the cricket field. I was 18, playing a game for my school's old boys' side. It was towards the end of the first innings, meandering somewhat, and I was fielding, keen but sunbeaten, at midwicket. A left-hander, the opposition's wicketkeeper, was on strike. It so happened that he played a ball semi-firmly into the legside and ran.
Now, the ball was coming into my left hand. I'm right-handed, so to attempt a run-out I would have had to bend down, pick it up, transfer it, spin, and throw. It all felt like too much effort. As it transpired, I never even bent down.
Reader, I do not lie when I say that from a 45 degree angle, somewhere approaching 20 yards from the non-striker's stumps, I swivelled and smashed a left-footed screamer into the base of middle stump, with the batsman a yard short. And then, knowing not how else to behave under such circumstances, pulled my cricket jumper over my head and ran around my disbelieving teammates, hooting with limited coherence.
I am mostly of the opinion that bygones are bygones, but I wouldn't mind that one being on Youtube for posterity.