GuyRule #246.5: Shotgun!
Shotgun should be called when either you first step outside a building or when it is decided by the guys that you are all going somewhere and are heading for the vehicle. Stating shotgun twice, (double-shotgun) negates your shotgun, 'cause either you didn't yell loud enough or you are not sure where you stand with the guys. Once shows that you are in control of the situation. -Joe Franceschi