be not all there
someone who is not all there seems stupid or slightly crazy

[TahlilGaran] Dictionary of Contemporary English ▲

not all there
not mentally clear.
He has periods when he's just not all there, which is a common symptom of his condition.

[TahlilGaran] English Idioms Dictionary ▲

not all there
to be not mentally adequate, to be crazy or silly
The man is not all there and sometimes he does very strange things.

[TahlilGaran] English Idioms Dictionary ▲

not all there
adj. phr. Not completely alert mentally; absentminded; not together.
Bill is a wonderful guy but he is just not all there.

[TahlilGaran] English Idioms Dictionary ▲