I agree that many animal owners are irresponsible. My cats have never been allowed outside simply because I can’t control cars, thieves, crazies, other animals, or diseases.
In this case, I think we can agree the owner was not correct in letting the cat roam, however, this “vet” was the one that ended its life in a very cruel way. Then, it appears that she thought it would be cool to show off.
Cruel? Cat didn’t feel a thing, most likely.
The vet was a jerk in multiple ways, but the owner has 100% of the responsibility for the death of the cat. The owner could have at the least spent a few bucks to put a collar on the cat so everyone would know it was a pet.