You Can Always Trust The Untrustworthy

You have to steal a chest from another crew and take it to the trading point. If you can be discreet, catching a ship on its arrival to an outpost, sneaking on, taking the treasure and sneaking around to the side back onto the outpost island would do it. Or go in with your crew guns blazing... Note that this is the opposite of Legends - "This is Unacceptable!". And that they could give you the chest...