I've defeated the Big Boss repeatedly, no badge. It seems absurd that I would have to get 6 stars for the badge when the level is so heavily luck based. Otherwise, wonderful game!
Great game. I'd just like to point out to people suggesting multiplayer that such a game already exists. Search Roadeo. One player players as the car, one as the road.
 "Kamikaze Pigs"){kind=icon}
 "You Are The Road - Molyjam 2012"){kind=icon}