Elephant
Elephants aren't predators and are known to help other animals and be socially active within their group. But while they're not in an epic war against humans, they can turn aggressive rapidly, especially as a result of their abuse and harassment by humans.
When caged or feeling the constraints of domesticated life, they can fall into a blind rage and have been known to kill their handlers as well as stampede tourists who show up to admire them. Some zoos have ceased all contact between human beings and elephants for this reason.