have rocks in head
have rocks in (one's) head
To be thoroughly stupid, crazy, absurd, incorrect, etc. You must have rocks in your head if you think the bank will approve you for another loan.
have rocks in one's head
Fig. to be silly or crazy. John is a real nut. He has rocks in his head. I don't have rocks in my head—I'm just different.
rocks in one's head, to have
To say or do something crazy, ridiculous, or stupid. This slangy expression, often used in a not very polite response to a bizarre statement or action, dates from about 1940. Presumably it accuses the person of having rocks instead of brains, as in “Drive all of two blocks to get the paper? Do you have rocks in your head?”