Using a word twice in a row isn’t always a no-no, but there’s always a more elegant way to revise a sentence in which you might initially be inclined to repeat a word immediately. When words collide, try these approaches:
1. “What you do do is your own business.”
Even if this sentence is intended as a counterpoint to a “what you don’t do” proposition, the emphatic first do is superfluous (“What you do is your own business”). If you must retain the repetition, introduce a separating phrase: “What you do decide to do is your own business.”
2. “They had had many arguments.”
Replace the second had with a prepositional phrase (“They had gotten into many arguments”) or a more specific verb (“They had endured many arguments”), or introduce more vivid imagery into a revision (“They had verbally sparred many times”).
3. “I showed her her message.”