In the Applewood Derby, Applejack, Rarity, and Rainbow Dash take over the CMC's carts and race them for their own desires. Everyone knows at the end that the girls apologized to each other, the race is done all over again, happy ending. Right? Wrong!
It will take three injured fillies and disqualification for these mares to learn their lesson. Basically an alternate ending where Applejack, Rarity, and Rainbow Dash actually get karma for being selfish.