This achievement is surprisingly easy for a 50G. I got this in the Create Contracts Tutorial, which started me in the Chinatown level. Walking into the mission area, I walked all the way straight, past the King (who’s the suited dude talking on the cell phone), and to the end of the map where there’s a female chef cooking up some stuff at a booth. To the left of the booth is a knife. I marked this lady as a target (since I was creating a contract), and picked up the knife. Pressing LT to aim at her from the side of the booth, I pressed RT and threw the knife at her. She died and the achievement popped, to my surprise. I suppose this would be one of the earliest points where you could get the achievement – I haven’t even started the story mode yet when I got this.
Hope this helps!