Our closest living relatives (evolutionary speaking, that is) sometimes gang up, sneak into another groups territory in order to find a vulnerable, isolated individual who they then proceed to tear to shreds through biting, clawing and a general pulling of limbs, for no apparent reason other than to show the others that they are not to be messed with.
Also, they sometimes go hunt for monkeys for no particular reason. They do eat them afterwards, but as chimpanzee diet is in no way contingent on meat (the hunting parties are so large that the amount of meat the participants get out of it is minuscule), nutrition is not the cause of this phenomenon. It has been suggested that they hunt for reasons to do with social display and political manipulation through how they share with and withhold meat from different members of their group. In short: chimpanzees are generally dicks to chimpanzees, and also behave like dicks to other monkeys in order to be even more dicks to their fellow members of species.