get (one's) head examined

What one is said to need to do if one does, says, or believes something that seems completely crazy, delusional, or stupid. You need to get your head examined if you don't think giant corporations are in control of our legislators! You spent $400 on a T-shirt? You need to get your head examined.

Also, have one's head examined. One is crazy or absolutely wrong. For example, You like this food? Go get your head examined, or If you believe that story, you should have your head examined. This hyperbolic and usually jocular expression of disagreement may, thought Eric Partridge, allude to the now discredited field of phrenology, which holds that the configurations of the skull reveal mental and emotional characteristics. [Early 1900s]