Baboon

Baboons are the most aggressive primates on the planet. When they feel threatened they flash their eyelids and teeth and are known to chase possible enemies in hoards. But they are known to fight each other just as willingly as they would fight another animal. They will kill each other over dominance of the group. Also the males are very violent towards the females, they will jealously guard them, grabbing and biting them when they wander too far away. Which is scary as the males are about two times the size of females.