Well, this was a little shocking. Me and a friend (Ferinex) were sparring (behind a building so clues wouldn't be visible), and as soon as the xp popup appeared, I clicked to walk away. However, he ended up being instantly permakilled somehow right about the time my guy took the first step away (It looked like combat ended - his portrat vanished, but he said on IRC he'd been permakilled).
We thought it would be a bit harder to permakill someone and that you wouldn't be able to do it by accident this way. For one we expected I'd have to hit him repeatedly while he was down before he died, for two, I thought combat would end after I KO'd him, and I'd have to retarget his body. Instead, I didn't even have time to end combat before my character permakilled him without my permission! D:
(And his body's irretrievable, so the items on it are also irretrievable, because it's behind that house)
Alternate Interpretation:
Your (presumably?) first DF-esque sparring fatality.