nobody home
nobody home {slang}
1. Your attention is somewhere else, not on what is being said or done here; you are absent-minded.
The teacher asked him a question three times but he still looked out the window. She gave up, saying, "Nobody home."
2. You are feeble-minded or insane.
He pointed to the woman, tapped his head, and said, "Nobody home."
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Source: A Dictionary of American Idioms