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1.
declared in a fight for shotgun (front seat of a car). when the car is in sight, passenger a yells, "shotgun!" reserving shotgun. in response, passenger b yells, "SHOTGUN CHALLENGE!" as soon as the second statement is declared, the two competitors must drop their pants to their ankles and run to the car as fast as they can. the first person to the car with their pants still around their ankles wins and gets to sit in shotgun.
*car comes into plain view*

passenger a: "shotgun!"
passenger b: "SHOTGUN CHALLENGE!"

*passenger a + b simutaneously drop pants and race towards car creating an amusing spectacle for all to see*
by pederson May 17, 2006
 
2.
A shotgun challenge occurs when a person call shotgun (front seat of car) to reserve his spot in the car. A second person snaps back with 'Shotgun Challenge!'. When this is done the two Shotgun Challengers must drop their pants/shorts where they stand and play a best of 3 Rock Papers Scissors match. The winner gets front seat.
Marie: Shotgun!
Mark: Shotgun Challenge!

(Both play rock paper scissors to see who wins 2 games first)
by Jaymizz13 May 01, 2008