have rocks in one's head v. phr., 
informal To be stupid; not have good judgment. 
 When Mr. James quit his good job with the coal company to begin teaching school, some people thought he had rocks in his head.
 When Mr. James quit his good job with the coal company to begin teaching school, some people thought he had rocks in his head.  [TahlilGaran] English Idioms Dictionary ▲