Easiest way to obtain this trophy:
Step 1: Load up the Campaign mission "Executive Order" on any difficulty.
Step 2: Follow Woods and obtain your Russian disguises. Keep progressing and meet up with Bowman and Brooks. (You will see them toss a couple Russian soldiers down an embankment.)
Step 3: When Woods says "just do what they do" you will see your team start running towards the main Comms building. STOP right where you are and do not follow your team to the building.
Step 4: Look to your left. There are 3 (three) enemies standing next to a building/wall. Equip your Python (default pistol you are given).
Step 5: Line up the shot and shoot the 3 soldiers that are standing next to that building/wall.
If for some reason you mess up, the mission will "fail" and you will restart from checkpoint.
Keep trying until you unlock the trophy!