I Call Shotgun!!

We've all done it. You're going out somewhere and you don't want to ride in the backseat, so you call shotgun to sit in the front. Problem is, someone else calls it as well. What do you do? Well, you could beat each other up until the last person standing gets the seat, or you could refer to the shotgun guide to see who gets it. I'd print out a copy and keep it in your wallet. You never know.