Dorothy learns that Sophia turned away her prom date John, who is now in Miami, because of the way he was dressed. When she told her that he stood her up, Dorothy lost all her self-esteem and went out with Stan because of this.
40 years earlier Dorothy was stood up for her by her prom date John, which affected her self-esteem. Now in Miami for a visit John tells her the truth: that Sophia was the one that turned him away. Dorothy is furious and blames Sophia for all the bad choices she made in her life.