Cool Dog is some kid named Max or something's cool dog. Or maybe Max is Cool Dog's court-ordained useless kid friend? He's so cool that he constantly listens to is own theme song on a personal ipod. He even has headphones because a dog can't wear earbuds. A savvy cool dog that knows his limits, he is.
There isn't much resembling a plot. Cool dog just does cool things for the whole movie, like saving kids and pilots who pass out after a "safe landing" that involves a lot of fire.
He beats up a gratuitous animal control officer.Edit
Cool Dog literally puts that joker in the trash. He is then put in a fucking dump truck as people either ignore him or laugh. Including the people putting him in. This is the penalty for defying the cool dog.