Near the end of the 'Pump and Dump the Junior Negotiator' quest, Frederik will mention his controller (SILHOUETTE), about 22:00 later that day she will appear at a small, previously hidden bar on Party Alley.
To find her, head to Dr. Gonza's clinic, and just a little south of his door will be an interactable section of floor that will pivot the camera to let you see Silhouette.
Start the conversation with her, and draw your gun (you do have a gun, right?) at the first opportunity. This will open a dialogue option with a coordination check to 'Shoot to wound' - you must fail this check to inadvertently shoot and kill Silhouette and unlock this achievement .