To get this achievement, you will need to be playing with someone who has already reached Rank 50. This is because once a player reaches Rank 50, they will have the ability to hire a Mugger for $1,000 through their in-game cellphone by calling Lamar. Take note that the player you are calling the hit on must have at least $5,000 on hand to get this done.
Set up a Closed-Friends Lobby and meet up in an enclosed section of the city with very few cars. The top floor of a parking garage or the desert of Sandy Shores works perfectly for this. After the Rank 50 player calls the hit on you, an enemy NPC will eventually show up, knock you down, and steal all your money. There will be a short delay before you are able to stand up, so pan the camera around to see where the Mugger runs off to. Once you get up, chase him down and kill him with whatever means are available to obtain the achievement.