Definition & Meaning of "have a screw loose"

What is the origin of the idiom "have a screw loose" and when to use it?

The origin of the idiom "have a screw loose" is not definitively known, but it is believed to have originated from the mechanical world, where a loose or missing screw could cause a machine or device to malfunction. It can be used to highlight eccentricities, irrational thinking, or unusual actions, often in a light-hearted or humorous manner, though it should be used with caution to avoid causing offense.