If it's just the death of animals, I've seen plenty. And when I say animals, I don't mean small, insignificant animal like insects and such, but mostly mammals, like cats, dogs, cows, sheep and more. Heck, I've slaughtered countless number of goat, sheep, cow and other livestock. Why? Because that's my field of profession.
I used to feel awful when I cut the neck of those cute cows and sheep, but as time passes, I don't feel a thing anymore.
As for human, I've witnessed the death of me dear grandfather (awesome person, he's one of my personal hero), my uncle, and the most tragic of all, one of my friend. This friend here, he died in an accident, right in front of me. He was run by a truck when we cross the road. It appears that the driver is sleepy or something, and he lost control of the truck. I managed to dodge in time, but my poor friend couldn't avoid it in time.
Ugh, I didn't even want to remember the condition of his body.