Well, it's a little complicated, but so it Twitter, and people figured that out in the end.
OK, so basically, it's 52 cards, a format we are all aware of. You place them face down around an empty glass as shown on your right, nominate someone to start, who flips any card, and let the fireworks begin. All players must be armed with their own poison.
There are 13 sets of 4 identical cards with specific drinking related actions attributed to each of the 13 different cards.
There is no winner to the game, only one poor unfortunate sod, who will have the misfortune of flipping the fourth and final GROG card. As the game progresses, every time one of these cards are flipped, the 'flipper' will pour a tot of his/her beverage into the glass in the middle of the table. So by the time the fourth GROG card is flipped, there should be an alcoholic concoction of at least 3 tots of whatever the respective GROG flippers' beverages were. The fourth GROG flipper (the loser) must then pour a tot of their beverage into the glass and down it (OUCH!!!) That terminates the game and you may then gather all the cards together and play again until you have had enough... (or fallen down)