use one's head
use one's head or {slang} use one's bean or {slang} use one's noodle or {slang} use one's noggin {v. phr.}
To use your brain or mind; think; have common sense. — Often used as a command.
If you used your bean you wouldn't be in trouble now.
Never point a gun at anybody, John. Use your head!
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Source: A Dictionary of American Idioms
