Wikipedia:BEANS

As the old story goes:

The little boy's mother was off to market. She worried about her boy, who was always up to some mischief. She sternly admonished him, "Be good. Don't get into trouble. Don't eat all the chocolate. Don't spill all the milk. Don't throw stones at the cow. Don't fall down the well." The boy had done all of these things on other market days. Hoping to head off new trouble, she added, "And don't stuff beans up your nose!" This was a new idea for the boy, who promptly tried it out.

In our zeal to head off others' unwise action, we may put forth ideas they have not entertained before. It may be wise not to caution against such possibilities. Prophylactic admonition may trigger novel mischief. As the popular saying goes, "don't give 'em any ideas". In other words, So, perhaps consider saying the following instead:

Keep your nose clean!

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Wikipedia