You can earn this achievement during the guardian hunter side quest that you get in vorago solitude after beating the final story mission. During this quest you will be asked to throw the trap grenades at the different types of guardians. At the end of the quest it will give you the choice to deliver the guardians or kill the master poacher. It is very important that you kill the master poacher otherwise you will not get the achievement. If you mess up and deliver then you either have to do the quest in True Vault Hunter Mode or dashboard to avoid saving.