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! We'll have to use our heads if we're going to have any hope of solving this supply issue.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
Use your head!and Use your noggin! and Use your noodle!
exclam. Think!; Think it through! You know the answer. Use your head! Use your noggin’, dogg!
See also: use
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.