Yes, this is a good thread...
My only regrettable killing was my first. It was a bunny rabbit and I had just bought my first .22 rifle. I sighted in on it without even thinking and only wounded it. I walked up to it and finished it off but it left a sick feeling in my stomach that persists to this day.
Now I'm very careful of what I'm shooting and why. If I have no plans to eating it, I don't shoot it.
Well, there was one exception to that rule. The year before last, Mal*Wart was razing an old factory to make way for one of their wonderful shopping boutiques. The factory had been abandoned for many years and a multitude of furry mammals had made their homes there.
The new construction had left all of these animals homeless. This included bears, beavers and, as it would happen, many, many rats, some of which found my yard to be a suitable replacement for their old home.
WELL, I located the patriarch of the group, a rat of impressive proportion, and pumped him full of .22 Aquila Super Colibri (575 fps). He ran away and I thought I'd missed him somehow or that the ammo was too wimpy. I found him the next day with three nicely placed holes in his side, dead as a doornail (whatever that means). That was one animal I had no qualms about killing in cold blood.