postal, adj. — Green’s Dictionary of Slang

postal adj.

[coined to reflect a spate of mass killings (of fellow workers) by disgruntled postal employees]

(US) crazy, psychotic.

1995

A. Heckerling Clueless [film script] I had an overwhelming sense of ickyness. Even though I apologized to Lucy, something was still plaguing me. Like Josh thinking I was mean was making me postal.

In phrases

go postal (v.)

(US teen) to lose one’s temper, to lose control of one’s emotions.

1993		St Petersburg Times 17 Dec. (Nexis) n.p.: The symposium was sponsored by the U.S. Postal Service, which has seen so many outbursts that in some circles excessive stress is known as ‘going postal’.
2004		C. Brookmyre Be My Enemy 250: If he’s a nutter and he’s gone postal, I’d say —.
2013		T. Black ‘Daddy’s Girl’ in Killing Time in Las Vegas [ebook] He was drooling as he waited for me to go postal.
2015		G. Disher Heat [ebook] Use them in a bank hold-up and they’d go postal—scream, punch, kick, fire off their shotguns.
2018		C. Hammer Scrublands [ebook] ‘The week before Swift went postal’.
2022		Twitter 6 July 🌐 Can you imagine how furious Big Dog [i.e. Boris Johnson] is going to be with another grilling like this? He hates being put on the spot and having his authority questioned.