Um, I hoped you have dumped that psycho ass.

Run and fast if he do that imagine what he do to you

I wouldn't just run it over, but I'd pull over, pull the shotgun out of my truck and put it out of its misery.

Break. Up. Now.

Your boyfriend is evil. Break up with him. And possibly slap him in the face for good measure.

You can not possibly be a decent human being if you are intentionally cruel to animals. Plus He knew you'd be upset and did it anyways.

The deer was screwed anyway. I'd have put it down too. If its on the side of the road, it most likely has been hit and has major internal bleeding.

Ok guys, I'm an avid animal lover, but the only thing that was wrong with this is that he had a smirk on his face. If it was a deer and badly injured, and lying beside the road, it was most likely going to lay there in agony for hours before finally dying. Sure it's gruesome, but sometimes euthanasia is the best solution, for the animal's sake. Unless he had a gun or something to inject the deer with, I would say he did the right thing.

While he may have been doing it a favor by "finishing it off" if he really drove away with a smirk on his face than at the very least you are dating a sociopath and at the worst he is a psychopath.

That's disturbing. You know what it says about people who enjoy being cruel to animals, right? In that situation, you should call the police non-emergency line, explain there's an injured animal in or near the road, and they'll either send animal control out or an officer to put it out of its misery