a law unto himself, herself, etc.

a law unto (oneself)

One who does whatever they desire and/or ignore rules and regulations. If you need to delegate, I wouldn't ask Gina—she is a law unto herself, and 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!See also: law, unto

a law unto himˈself, herˈself, etc.

a person who does what they want, even when this is against the rules and customs of a group or society in general: That man is a law unto himself. He comes to work when he likes, and when he’s here he doesn’t do what he’s supposed to do.See also: law, unto