I have had to dispatch 3 x animals in my time.
1.
I hit a roo doing about 30km/hr on the driveway of our golf club and broke it's legs. I didn't want to kill it, but watching it try to get up with broken legs was not pretty. Also, being on the driveway, it was about to been by a lot of people, so I found a big stick, and whacked it as hard as I could over the head. It died instantly, and I dragged it out of sight.
2.
I was riding my dirt bike, when a roo jumped across the track in front of us and went head 1st into a fence. It was clearly buggered, but still kicking. We grabbed a big log and dropped it on its head. It died instantly.
3.
We were camping in a Game Reserve near Renmark when we came in contact with a feral cat. I decided to kill it as it was hanging around our camper and passing on things. This prick of an animal was the most difficult to kill, with the back of an Axe and my steel cap boot. It did not die quickly, and I felt sorry for it, but once I started the process, I felt that I should finish it.
These are the only animals I have killed, (apart from fish & worms) & I didn't enjoy killing them, but in each case, it was the right thing to do.