The term "shotgun" or "calling shotgun" derives from the days of cowboys and stagecoaches. The man riding "shotgun" actually rode up front with the driver and carried a double-barreled 12 gauage "coach gun" that was used to defend the passengers of the coach from indians and highwaymen, etc.
Now-a-days, "Shotgun" means the guy who gets to ride up front with the driver, and all the status that's implied with said seating. To ride "shotgun" tells other people that, aside from the driver of the vehicle, you're in control; you have all the powers that the driver does except for driving the vehicle. Nay, some could even argue that you're more powerful than the driver because he has to remain focused on the road, while you get to fiddle with the radio, your phone, your iPod, your computer, etc. You also get the best view, and people tend to think you're more important than the poor sons of bitches in the back seats, forced to look at the back of your skulls for the duration of the trip.
But there has to be rules to calling "shotgun", lest you engage in an actual "arms race" with your fellow passengers.
Yes, we all know the "can't call it before you see it" rule, which implies you have to actually see the vehicle in question before calling it. And of course you have to respect the first person to make the call, even if they've been calling it all day like a total dick.
But there are other, often over looked rules to "shotgun" that fall to the way side. How about "deferring to seniority" meaning that a good car mate should give the eldest rider at least a chance to call "shotgun" while walking across a mall parking lot, well within the sights of the vehicle? To this I would suggest that if you're practically on top of the vehicle and they still haven't called it, then it'd be acceptable to nonchalantly "call it." Calling it excitedly makes it sound like you were chomping at the bit the entire time we were walking and not paying attention to my story about the Victoria's Secret sales lady hitting on me.
How about the "door handle" rule, where, if you call "shotgun" and my hand's on the door handle to the front passenger seat, all bets are off. You dare call "shotgun" when my hands on the handle, or even - Jesus, the door's open, I'll probably shoot you in the stomach, and we can reinact the scene from "Resevior Dogs" where Mr. Orange is bleeding to death in the back seat.
In the back seat.
And then there's the two rules which negate calling every time: The "my shit's in the front seat" rule, and the more precident "this is a two-door coup and I'm being dropped off first" rule. The latter is self explainitory, however the former seems to get over looked all the time. Listen, if my shit's in the front seat, whether it's my iPod, or purchased items, or a sweater, fucking leave it there and let me take my seat. The only way this rule can be vetoed is if by some chance, you can prove I left my shit in the front seat on purpose to act as a place holder.
Which I invite you to try, Balls Mahoney.
I'd also like to dicuss some of the over looked responsibilties of the co-pilot riding "shotgun:" When stopped to get gas, the shotgunner should get out and clean the windows. If you think you're slick enough to jump my seat while I'm out of the car, cleaning it, then god help you when I get back into the car. I'll be sitting behind you, making your life a miserable Dante-esque-9th-Ring-Hell.
Other responsibilities include: when pulling up to a toll booth and the driver doesn't have an E-Z Pass, they fish for the change or pay the toll out of their own pocket. Also they clean up all front seat trash accrued through the trip.
And of course, should the vehicle be overrun by blood thirsty savages, they lay down a heavy barrage of gunfire to cover the escape.