I smashed the rat
Why did you smash the rat?
I hate rats, they are disgusting. That is why I smashed it.
Well, if you caught a rat in your home, it is understandable that you want to get rid of it, one way or the other. It is okay to kill pests.
I just wanted to smash it good and destroy it. I see no problem with it.
Yes, I think your actions were justified when it came to killing an unwanted pest, but I worry about how much pleasure you are taking in it. The best way to rid your life of pests is prevention, so take extra care to clean up any leftover crumbs, and plug any holes in your walls.