Lose (one's) marbles phrase
"Marbles" is a term for a person's mental faculties.
To be or become unable to think normally; to be not responsible for one's actions due to a mental illness.
He escaped a prison sentence on the ground that he lost his marbles at the time the crime was perpetrated.
Look at that car! It is traveling at break-neck speed! The driver must be losing his marbles!
Stupid or crazy
If you're off your trolley, your ideas or behaviour are crazy or insane.
Suddenly become crazy or very angry or lose control
Totally insane; overflowing with emotion, especially rage or enthusiasm
The verb "lose" must be conjugated according to its tense.
This phrase was formed based on the meaning of the noun "marbles," which probably originated as early 20th-century American slang.
Someone who is totally bad at doing something.
Mary really can't sing for toffee.