Some potential options
Write a poem or story using a lot of metaphor that sounds like nonsense but has a much deeper meaning.
Write something that is actual nonsense, means nothing.
Write about the day to day nonsense you have to put up with from other people.
Write about an argument or confrontation you had that degenerated into nonsense.
Write about a person who is full of nonsense and drives you crazy.
Write about a romantic situation that completely turned your life upside down and made you feel as if you had lost your mind.