This is: a brick.
It is the preferred messaging device of "the mob." Its usage is simple. First, write a message on it, or affix a message written on something else to it - such as a bit of paper, or a finger. Then, grasp it firmly in your hand, and throw it one of two places - either at the receiver's head, or other vital bodily part; or somewhere where said vital bodily part will be at some time in the future. Other projectile messaging systems include the arrow, the rock, and a small man in a large catapult.
