Nutcase (noun)

A person who is considered to be insane or mentally unstable.

Origin:

Derived from "nut", meaning "crazy" and "case", referring to a person. first recorded usage in the early 20th century.

Examples:

1. The man on the street corner ranting and raving was clearly a nutcase.
2. After her breakdown, she was committed to an institution for nutcases.
3. He has been labeled as a nutcase by his colleagues due to his erratic behaviour.
4. She's such a nutcase, always acting out in bizarre ways.
5. He"s a complete nutcase, you can"t trust anything he says.