double-pump shotgun 

The term that is used for someone willing to take the seat of a (usually) retarded person who calls "shotgun" in an attempt to obtain the front seat of a vehicle. However this must be said within a split second subsequently after the first person calls shotgun.

Person 1: "I call shotgun!"

Person 2: "Well I call double-pump shotgun, better get in the back of the van or it's gonna be one hell of a ride for you."

double-pump shotgun by ogdajuiceman February 20, 2011