Explaining “You must have rocks in your head”

What does it mean?

The phrase "You must have rocks in your head" is an idiomatic expression used to suggest that someone is acting foolishly, lacking judgment, or not thinking clearly.

Tone

Origin

The exact origin is unclear, but it is thought to have emerged in the English-speaking world in the early 20th century as a metaphorical expression implying that one's head is filled with useless material (e.g., rocks) instead of rational thought.