noun

1. A person who is psychotic or otherwise insane.

   “The loony bin up on the hill is full of psychos.”

2. A person who acts in a bizarre or dangerous manner.

   “She complained that he was a psycho for driving at such a high speed in heavy traffic.”

Synonyms: creep, freak, loose cannon, weirdo, freak, loony, nutcase, wacko

adjective

1. Psychotic, or otherwise insane.