be a law unto (oneself)
To do whatever one desires, irrespective of existing rules, regulations, or expectations. If you need to delegate, I wouldn't ask Gina. She is a law unto herself, so it's hard to persuade her to do anything she's not interested in. How many times has Jason been arrested now? Geez, he sure is a law unto himself! The country will be met with swift sanctions if their president continues to be a law unto himself.
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