An event that involves using a flashlight and a pillow on an unsuspecting sleeping person, where you whisper "There's a truck in the road" and you repeat the phrase over and over again with increasing volume, while flashing lights in their closed eyes. Eventually you shout "The truck is here!" and when the sleeper sits up, you whack him or her with the pillow.
At summercamp, trucking is customary on the last night of the summer; especially with the campers you do not like.
When someone is on LSD and you take a pillow and a flashlight, run at them with the flashlight on and hit them in the face with a pillow. then, yell, "TRUCK!" usually is followed by the person thinking that they were hit by a truck. Person trucking+good trip=bad trip.