keep nose clean
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keep (one's) nose clean
To behave properly; to stay out of trouble. You better keep your nose clean, kid, or you're going to run into trouble you can't handle.
keep one's nose clean
Fig. to keep out of trouble, especially trouble with the law. I'm trying to keep my nose clean by staying away from those rough guys. John, if you don't learn how to keep your nose clean, you're going to end up in jail.
keep (one's) nose cleanInformal
To stay out of trouble.