Inverted: Bob treats Alice like his daughter, except with sex.
Bob pulls his weight around the house.
Alice, sick and tired of this status-quo, adds poison (or maybe just Blazing Inferno Hellfire Sauce) to the sandwich in hopes of getting rid of Bob or making him want to get off the couch and make his own damned sandwich.
But then comes down with the flu and expects Alice to drop everything and take care of him.
Bob decides he doesn't want this kind of sandwich and whines until Alice makes a new one for him.
Alice gets up to tend to her crying baby, and then hears Bob crying in the living room because he dropped the remote.
Alice asks Bob to take out the trash, and he pouts and stomps and says "No!" like a 2-year-old, complete with eventual tantrum.
Bob acts childish but when it counts, he acts quite mature. The second he can though, he reverts back to actings like a manchild.
Bob and Alice intermittently parent each other.
Alice and Bob are equally responsible (or irresponsible) around the house.
Alice and Bob are not living together. They may not even be married.
Invoked: Alice marries Bob, who is blatantly a Manchild.
Defied: Alice breaks up with Bob during the dating stage (or divorces him) when she sees that he is just too childish to qualify as a good husband, and that a) he isn't likely to change anytime soon and b) she sure as hell can't change him.
Reconstructed: Alice and Bob both pull their weight around the house. Alice learns to say no sometimes, and Bob takes responsibility. The relationship is running smoother, and Alice doesn't feel resentful or "used" or stressed, or taken advantage of. And Bob has a sense of purpose and more self-respect.
Played For Bow-Chicka-Wow-Wow: Age-play; for example, Bob wears an adult diaper and acts like a baby, and Alice cares for him, followed by sexual favors. (As always, this can be Fetish Fuel for some and Distilled High-Octane Squick for others.)