Just off the top of my head, maybe a role reversal? Like, how about this: Marge goes out of town for the weekend to visit relatives, or something, and leaves Homer a list of chores to do. Homer, as usual, farts around and does none of it until the night before Marge comes home. Then, in a burst of love for his wife, Homer groans and reluctantly begins to clean the house.
He finds, to his surprise, that it's rather relaxing and satisfying to clean, cook, and tidy up. It puts him in a good mood. So when Marge comes home the house is spotless. Marge is impressed, and Homer asks her if he can start helping out with housework when he's not at work.
Marge agrees, but Homer is TOO good at taking care of the house. He's so good at cleaning, cooking, grocery shopping, and more, even in his limited time outside of work, that Marge suddenly finds herself with nothing to do all day. This causes her to, ironically, start adopting some of Homer's behavioral traits: she constantly sits around on the couch drinking beer and watching TV. She begins to snack more as well, and gradually progresses to eating whole extra meals, purely out of boredom.
So by the final ten or so minutes of the episode their roles have, essentially, been reversed: Homer is now the fastidious busybody who keeps up the house, and Marge is the lazy fat fuck who sits around and does nothing all day. Lisa becomes disturbed at this, and so she conspires to get Homer to go back to his old ways to save Marge from herself.