Takes only a couple of minutes!
If you did not onlock this achievement during the game you can easily achieve it by selecting a new world with your existing character. You will keep your progression and equipment. Just make sure you equip the arc rifle from your existing game and go to the main menu. Select solo campaign, select your agent and start a new world. Skip the cutscenes and make your way to the hideout of the first boss, Berg. Before you enter and start to fight him. outside are some enemies that are easy to kill. Just make sure that three of them are in a straight line and and shoot the first one. The other two, behind him, will be electrocuted as well and the achiement is yours. If you fail, inside are more of these enemies and you can it there again.
Good luck!