A metaphysical punch. Sometimes a real punch can be called a booker, but not all punches are bookers. A booker is therefore an expression used to define the impression made by an action or thought.
This definition stems from the fact that a US county sheriff can, if you do do something stupid in his presence, such as resisting your arrest, book you a ticket to the slammer or big house.
boy a): yay. just heard flying agaric is a pleasant experience. Let's try it.
boy b) why in the devil's horn are you so proud of yourself? I bet it would be a laughing matter, if a booker pulled you over and booked you in the slammer for the night, wouldn't it?