At the very start of the game you find yourself in an alligator farm.
if you head outside you can jump into the water and get eaten by the alligator which will reward you with this achievement.

At the start of the game you can find two people in the room with the keys.
You can either chuck the already dead body into the water outside the building, or you can choose to kill the guy sitting on the chair and chuck him in, if you want, or both.