(Strip Number 724, Original Publication Date, 11 October 1984)
Panel 1: We find Mike and Lizzie doing what they love best: calling each other insulting names because they can't stand the sight of one another.
Panel 2: For some reason, Mike calls a halt to the curse warfare.
Panel 3: Said reason looks in on them as Elly finally shows up trying to figure out what's disturbing her staring off into space wondering if there's more to life than chasing after children. Mike and Lizzie smile plastic smiles to make Mommy go away.
Panel 4: After Elly leaves, Mike asks where they were before Mommy tried ruining their fun.
Summary: Most of why Mike and Lizzie hate one another is that they're the creation of a woman who sees life as a pitched battle for supremacy between the sexes in which the female of the species is supposed to feebly wail about her total inability to win anything. (Hint: this is why Mike thinks that brothers never fight. Since they're on the same team, it makes sense to him that they stick together.)