The worst place to have to go and wait. Usually directed to misbehaving children, intoxicated friends, or overly-flirtatious significant others. In this context, "the truck" is a lot like Purgatory; it's not punishment exactly, but a place to keep one out of trouble and allow one to think on one's sins before one goes home and one's exact fate is decided. Being told to wait in the truck is only heard when one is away from home, and usually when one got to one's current destination by riding in a truck.
A misbehaving child has just poured Dad's Jack and Coke all over the dog.
Dad: Dammit, Billy, I told you about that! You go wait out in the truck.
Sober Driver: Jackie, for Christ's sake! I told you you had too much to drink, now. Get, go on back. Go wait out in the truck, and stay there this time.
Wife: Look here, now, do you want to go wait out in the truck? Stop staring at that hussy's behind.
Most commonly heard in the Southern tier of the United States, though instances have appeared as far north as Fort Collins, Colorado, near the Sundance Steakhouse and Saloon on quarter-drink night.