How much Guinness beer is used in an Irish Car Bomb?

The correct amount of Guinness beer used in an Irish Car Bomb is indeed 3/4 of a mug. An Irish Car Bomb is traditionally made by dropping a shot glass filled with a mixture of Irish whiskey and Irish cream into a pint of stout beer, usually Guinness. The recipe calls for a substantial amount of stout to balance the potent flavors from the whiskey and cream, providing a creamy counterpoint to the sharpness of the alcohol. Using 3/4 of a mug ensures there is enough beer to create a satisfying and balanced drink while allowing for the dramatic effect of dropping the shot glass into the beer. The other amounts are either too little to properly embrace the drinking experience or too excessive, which would detract from the intended balance of the drink.