lose one's marbles
idiomPart ofmarble
lose one's marbles — idiom
1. to become crazy or mentally confused, especially as a result of old age
1.idiom
Definition
to become crazy or mentally confused, especially as a result of old age
Example
Grandfather keeps talking to the television — I think he is losing his marbles.
Anyone who tries to climb that wall in the rain must have lost their marbles.