go postal: become irrationally violent, usually from work-related stress

On August 20, 1986, Patrick Sherrill, an Edmond, Oklahoma postal worker, killed fourteen of his fellow employees and wounded six before fatally shooting himself. Sherrill's killing spree is generally attributed with inspiring the term go postal. However, several copycat incidents involving postal workers who were fired or forced to retire might have contributed to the expression's spread. By the early nineties, go postal was well entrenched in the vocabulary. Its earliest known appearance in print is in a St. Petersburg Times article for December 17, 1993. The Times reports that the U. S. Postal Service is sponsoring a symposium on workplace violence. The article notes that the Post Office has seen so many recent outbursts "that in some circles excessive stress is known as going postal."

The Postal Service, understandably disturbed by this negative publicity, made a broad-based survey of occupations and concluded that working at the post office is one of the safer ones -- far safer than driving taxis, for instance. The report comments, "If 'going postal' is meant to suggest that postal employees are more violent than the national workforce, it is simply untrue."

Since at least the late nineties, go postal has lost its connection to both the workplace and lethal violance, and can now refer to any kind of rage. It is increasingly used to mean an ordinary loss of temper, as in If my mom catches me surfing the Web when I should be doing my homework, she'll go postal.