I just killed my fish
Why did you kill your fish?
I thought this was the best time to kill him since no one will notice
Wow, that just doesn't seem right. How do you plan to explain what happened to the fish?
No, I'll just tell people that I donated it to science or something.
Killing a pet for fun is not reasonable if it was not suffering. If you have plans to hurt others I think it might be good to seek professional help.