You can watch a complete run through in the video below, from Influx on YouTube:
Helpfully you'll sober up pretty quickly into the journey, so completing it should just involve a simple drive, though sadly there no special reward for finishing this job. It transpires that you stole a delivery truck in your stupor, and the secret Casino Work mission that begins here requires you to return the vehicle to the casino before the time limit expires. If you do, you'll revive at the side of the road, before casino manager Ms Baker calls you up and lambasts your drunken behaviour. Normally, you'll wake up in a random location, such as in your bathroom or on your bed, but if you roll the dice enough times then you might just get lucky and find the secret GTA Online casino mission 'Damage Control'. Order a Macbeth Whisky Shot, and shortly after drinking it you'll collapse and completely black out on the floor. You need to hit up either the main casino bar or the one in your Penthouse suite (if you've purchased that upgrade) – the Penthouse bar is the easier option here, as you can quickly sprint back to it after completing the next step. The method for accessing this secret GTA Online casino mission is very similar to how to get the Kifflom t-shirt in GTA Online, except you do it in the casino rather than a nightclub.