Update: Thanks everyone for the Positive reviews
*Must have wire cutters
A very simple way to do this is in chapter 3 in the brothel. You will come very early in the mission to a room with an opium tank with 2 ladies in it. You will know you are in the right room as Garret will make a comment about overloading it. Pick the door upstairs and make your way around to the panel in the back. Use the wire cutters on it. Go back to the front and hit the switch next to the opium tank overloading it. Achievement will pop almost instantly even if you have never used the environment before. 10 plus knockouts.
*If your playing on Master Difficulty you will fail immediately so make sure you save your game before hand.
Youtube link provided and credited to Dejected Santa