The term most probably comes from the Native American use of a device called a "
Coup Stick". As a
symbol of bravery, a
warrior would often take a stick into
battle, instead of a
weapon. By touching a foe in the heat of battle, the
brave proved that he was skilled enough to close with the
enemy and touch him without getting hurt. It was also used when
taunting the enemy, literally shaking a stick at them in
contempt. This was called
counting coup.
In modern usage, the term has come to mean an impressive array of goods or a situation not easily dismissed by waving one's coup stick at.