Taking everything out of a backpack, flipping it inside out, putting the books back, and then zipping it back up. Usually done when a friend goes to the restroom during class or leaves their backpack while they go to buy food. This can also be done by stuffing the backpack into the small pouch it has in the front and zipping it up.
The skill of being a dumbass and smarting off to a kid eating a chili and cheese burrito, then having the kid throw that burrito at you and having it explode on your back and go all over you and your truck.