Biff lied man!!
I believed in Biff!
I trusted Biff!
Biff let me down...that jerk!
It occurs to me that the 2015 that Marty visited in the movie was altered when Marty failed to get into that car accident he was supposed to have. Maybe the driver of the other car was killed in original reality and that driver went on to father one of the Mets star players, thus preventing the Cubs from winning. ;-)