You unlock this one in Brooklyn Bridge Station, but there's also a need to have a full inventory, so if you've reached this point in the game with more than 4-5 empty 1x1 blocks in it, you probably won't be able to unlock this achievement on this run.
On one of the four ends of the ground floor of this area you'll find Rock, a heavily augmented drug dealer. Kill him whichever way you see fit. Pick up all his items from his corpse. You need to make sure JC cant' receive any more LAMs. That's done by having a full inventory without any LAMs in it. If you have even only one LAM, JC will stack them. So, drop them if you're carrying any and search all the rooms on the ground floor, you can find some forty's, sodas and flares to fill up the inventory. Items you drop stay there for as long as you're in this chapter, but you can always save before dropping any actual useful items you might want to keep for later in the game. Once you're full or almost full, go upstairs.
Find the Rooks' leader, El Rey, who is on one of the two ends of that floor, but don't talk to him unless your inventory is full. There are more items you can use to fill it up in the room he is in. Once you're set, talk to him and he will try to give JC the LAM as a reward for killing the drug dealer, but with the inventory being full that's impossible. Once you're in control of JC, talk to El Rey for a second time and that will trigger the dialogue that in turn triggers the achievement.