True to their group name, they have monkey tails and act much like the said animals.
History
When the Straw Hat Pirates visit them, they are drunk because their prize slave catch, a giant, was for nothing because Peterman took a mermaid to the Auction House after them. The only reason that they caught the giant was due to him being asleep at the time but it was very difficult for them to carry him to the auction house.[1]
The leader of the Coffee Monkeys somewhat resembles the main character of "Journey to the West", Sun Wukong, the Monkey King who wields a magic staff and is often depicted wearing a gold headband.
All members of the Coffee Monkeys share the same birthday: November 14th.[3]