At first these guys are passive and tame and can be given any type of berry. (Mejoberry is recommended) do not run up to its face. It will run away and it will keep running.(other monkeys near it will also run away too) simply crouch and feed it berries. Once tamed, they will love you forever.(they are a shoulder mount so put them on your shoulder and take them EVERYWHERE) they have a really cool ability to through poop at the enemy that is chasing or if it is your target. When it through the poop if it lands it will disable there ability to sprint for a little while.( and will take small amounts of dmg too while the poop is on them). I hope you found this guide helpful.
Always stay crouched while taming. And never get close enough to touch it. While following the monkey, if the monkey ever stops, its very likely It will turn and start to walk in a different direction. So be aware that it might walk in your direction. Hope this helps : )