[Don’t go postal on me–I haven’t inflicted one of my phrase-origins on you in quite awhile.]
If your friend is so stressed out that he suddenly flies into a violent rage, you may accuse him of “going postal.” What does the post office have to do with it? A lot.
In the late 1980s, there were several deadly events involving U.S. Postal Service workers. In 1986, the first event, an Oklahoma postal worker shot 20 fellow workers, killing 14; then he shot himself. After that, and up to 1997 there were 20 other similar events, killing 40 people, including some regular citizens. In the middle of this, in Dec. of 1993, The St. Petersburg Times reported that some people were referring to what was happening as “going postal.” Thus, the term was born.
By the way, long-term studies indicate that working for the Postal Service isn’t any more or less stressful than most jobs.