You can get this achievement early in the DLC. As you progress through the first location, you will come to a back yard with the plank over the side of the ship, there's a pirate on it pushing a human over. Kill the pirate (push him over for another achievement) and then jump off the plank yourself, winning the achievement and killing yourself in the process.
(if you don't know how to access the dlc, you will need a LIFTER HOOK - so progress through the main campaign enough to get it, then head to Port Nixon, down the exo lift in the Iron Maus store and in the open area near water you will see an orange boat. It will take you to a small islet from which you need to use the lifter hook)