Jigglypuff is well aware of the effect of its song and cheerfully uses it as leverage to get what it wants. No more dessert? It sings and steals its neighbor's. Souda not spending enough time with it? Sing and knock out all the other Pokemon. Being forced into chores? Sing and run away! Whenever anyone scolds it, it tears up tragically and squeaks about how it just wants to show its appreciation by singing a lovely song... which it will promptly demonstrate to get out of trouble.