rocks in one's head, to have

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.
See also: have, head, rock
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

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?”
See also: have, rock
The Dictionary of Clichés by Christine Ammer
See also:
  • have rocks in one’s head
  • go to one's head, to
  • crazy in the head
  • head in
  • hold a pistol to (one's) head
  • a head
  • fat
  • good head on one's shoulders, to have a
  • hit the nail on the head, to