Gimme a Break! (1981)

Season 2: Episode 8

Julie invites a handsome boy at school to come over to stud with her, but he falls for Katie, and the two go out. When Katie comes home, Julie and her have it out in a hilarious catfight of sister versus sister. In the end, Katie finds out that the boy knew Julie was Katies sister and wanted to go over the house so he would get a date with her. Katie and Julie final make up when Katie tells Julie what the boy told her.