[frank ballenger]

I think that technical psychological term may be too abstruse for lay persons. /S

Maybe “his elevator doesn’t go to the top floor.”
or “he has toys in the attic.” “gone fishing” “has bats in his belfry”

Or....

https://mugbarista.com/products/the-far-side-just-plain-nuts-mug-oz

[NonValueAdded]

or “his cheese has slipped off his cracker.” /GreenMile