Can be found here. This squares with the way pretty much everybody I've met who wasn't from Randolph does it.

In Randolph we did it a little differently. Because the group of debaters I hung out with shared at most one brain -- and because we always stayed too long at places anyway-- "It's time to leave wherever we are" was generally declared by one person's suddenly calling shotgun.

If it was truly time to leave, the rest of the group agreed by acclimation*, shotgun was awarded, and everyone began getting ready to go. [EDIT: For brevity's sake, I left out a step. See comments.]

If it was not yet time to leave, that was agreed upon by acclimation too, the false shotgun-caller was mocked, and everyone stayed where they were.

It was a good system and it worked well. And I've never really adapted to the "Shotgun must be called outside while in view of the car" rules that operate throughout the rest of the planet. Luckily, as I've gotten older, I'm always either the driver or the driver has a significant other, a state of being which has rendered the technicalities of the shotgun contest largely moot.

I guess this is growing up.