use your head

use (one's) head

To use one's own intelligence and intellectual ability; to think logically and rationally. In this phrase, "head" refers to one's brain. Often said as an imperative. Come on, Dean, I know you can figure this out on your own. Use your head for a change!
See also: head, use

use your ˈhead

(British English also use your ˈloaf) (informal) think carefully; use your intelligence: Use your loaf! Meena can’t read English, so there’s no point in writing her a letter!In rhyming slang, loaf of bread stands for ‘head’.
See also: head, use