Definitions:

1. Describes a person who behaves in a way that is considered wildly irrational or crazy. NOUN
   • We encountered a nutcase on the subway who was yelling about aliens invading Earth.
2. Refers to someone whose actions or thoughts seem very unusual or eccentric. NOUN
   • My neighbor is a bit of a nutcase; he spends his days talking to his plants.

Synonyms:

• crazy
• fool
• lunatic
• maniac
• psycho
• psychopath