Some were accidental..some weren't..well usually to common Pokemon I might make them faint if they make my Pokemon faint..but other times they're usually either because of the level differences or because of critical hits..and that is the one time I don't like seeing critical hits..I've done it to a few legendaries accidentally because of critical hits but those don't usually bother me as much as doing that to a Pokemon I really want..

Yeah when I was trying to catch Latios, my Crobat ACCIDENTALLY hit it with a very powerful Air Cutter and when I was also trying to catch Latias, Wobuffet unleased a one hit KO Mirror Coat on it, it made me very dissapointed, I guess I should not have sent out both my Lv 99 Pokemon to confront those Legendaries...

good times of how many kill my pokemon did and then i will scream at my ds in anger good time:)

It happens a lot with me TT
Ii had to try to catch my Giratina FOURTEEN times 'cause he faint a lot.

when i was tring to catch bulbasour and i sent pikachu and used its thunderbolt then bulbasour fainted with one shot

The HORROR of KOing a shiny...

Soft Reset ftw aka: plenty of times

A lot of times.

I have a few times
i once accidentl did it 2 latias on Sapphire or Emerald so I cut the game off.
i always save b4 I fight legendaries (just) in case something goes wrong.

yes, even to a legendary pokemon i accidently made it faint:P