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.” Thirty-five people have been killed in 11 post office shootings since 1983.
(deyim) Meaning: Go mad, go berserk. Origin: Originated in the USA in 1990s, where there were several incidents of people going berserk and shooting numerous members of the public in post offices