You can get it in the TAIGA level after you clear the last Pirate camp by lifting the gates and sailing a boat through them. Don't worry, triggering this achievement won't interfere with the Forrest Child achievement as Admiral is not counted as an enemy and you won't need to fight him at all.
You will then arrive at a Sawmill area, which you will recognize by all the toxic gases that necessitate a gasmask, and shrimp enemies attacking you. You need to get to the top of the Sawmill by using the elevator in the half-flooded main building. To get that elevator to work you need to first activate the generator that is situated in the shack to the right of the main building - luckily it is the only generator in the game that already has enough juice to fire right up so you don't have to look for a canister.
Afterwards follow the wires to the switchboard in the top left corner of the main building and switch it on. Then walk over to the elevator in the middle right of that same building and take it up.
Once up there you will face a door which you can kick open to meet the Admiral. Lower your weapon and sit down at the table once he (or rather one of his friends) mentions it - he kicks a chair over to you. Then sit down, have a couple of sips of tea (don't worry, there are no side effects), and listen to him and his companions speak for a while. Eventually he will ask his friend to play the guitar but the guy clearly doesn't want to, so pick it when the prompt appears and play for a bit. At that point the Admiral will light up his pipe (you don't need to smoke even though you are given a prompt) and eventually fall asleep, at which point the achievement should pop.
Loot the room and cut down a rope ladder in the corner. You will then be able to rappel over to the next location and continue with the level.