This achievement should only take a few minutes. Start up the first chapter "Last Call" and in the bar go to the arcade machines. One of them is a black jack machine. Save your game in front of the machine. Now do the following until the achievement unlocks:
1. Bet everything you have
3. If you win, save. If you lose, reload the previous save
4. Go to step 1
For a short explanation of the rules of Black Jack, go to http://en.wikipedia.org/wiki/Blackjack
or read the quote below.
"The basic rules of the game involve adding the value of an initial two card hand in hopes of being dealt a value of twenty-one. If a value of less than twenty-one is dealt, the player may choose to be dealt single cards until they either reach a value of twenty one, reach a value they feel comfortable to play, or reach a value that exceeds twenty-one. The winner holds a hand with a value of, or nearest to, twenty-one without exceeding it." - Wikipedia