In the drinking game "Kings," the Thumb Master is the player who is in charge of signalling when someone must drink. At any point during the game, the Thumb Master can put his thumb on the playing surface (table) or forehead. Everyone else must also do this, and the last person that does it has to drink. One is bequeathed this role when he pulls a 10 (or whichever card is deemed). The Thumb Master rules until the next person pulls a 10, in which the new person inherits the title.
I wasn't paying attention when the Thumb Master put his thumb on the table; therefore I had to drink!
When playing the drinking game, King's Cup' (or 'Ring of Fire'), if a certain card is drawn by a person that person becomes the thumbmaster, and whenever they place a thumb on the table or floor everyone else in the circle must follow, and the last person to follow must drink.
Fred is thumbmaster. Fred places his thumb on the table. Everyone except Georgie notices and follows. Georgie is last, so she must drink.