off one's head

Prepositional phrase

(UK, Australia, colloquial)

1. (Australia, UK, colloquial) Insane, crazy.

   Synonyms:

   off one's chump

2. (Australia, UK, colloquial) Temporarily mentally unstable; very distressed.
   • The kettles they boiled with rage, 'tis said/While ev'ry nail went off its head[…]1881, “The Magnet and the Churn”, William S. Gilbert (lyrics), Sir Arthur Sullivan (music)
   • When I had finished I went and saw poor Leo, who was quite off his head, and did not even know me.1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887, →OCLC
3. (Australia, UK, colloquial) Under the influence of drugs.
   • Occasionally they seem to go off their heads. Something like epilepsy, you know. It's called Robot's cramp. They'll suddenly sling down everything they're holding, stand still, gnash their teeth—and then they have to go into the stamping-mill. It's evidently some breakdown in the mechanism.c. 1921 (date written), Karel Čapek, translated by Paul Selver, R.U.R. (Rossum’s Universal Robots): A Fantastic Melodrama […], Garden City, N.Y.: Doubleday, Page & Company, published 1923, →OCLC, Act...
   • The music is turned up over the conversations, which span global politics, the latest Beyoncé track and anything else randomly entering the minds of us intelligent, but off our heads, savvy young adults.2017, James Wharton, Something for the Weekend, Biteback Publishing, →ISBN

   Synonyms:

   off one's face