This article is part of Yahoo's 'On This Day' series
When we hear the phrase "going postal", we assume it's in reference to someone displaying extreme anger or aggression.
While this phrase is commonplace nowadays, its origins have much more sinister roots.
On this day in 1991, "going postal" became a commonplace saying when a US postal worker committed two brutal murders.
A ticking time bomb
In 1990, Joseph M Harris was an average 34-year-old postal worker in Ridgewood, New Jersey.
Described by neighbours and co-workers as “quiet”, “tense” and “odd”, Harris apparently had a temper.
One former co-worker remarked that during work hours “he was always walking around like some karate guy, chopping his hands in the air."
Harris did not respond well to authority and directions, and consistently clashed with his supervisor Carol Ott.
Their feud reached its peak when Ms Ott filed a report with the Ridgewood police department, accusing Harris of harassing her on the job.
She then ordered for Harris to submit to a fitness of duty exam, which he refused, and he was ultimately fired.
Other postal workers recalled Harris saying something to Ms Ott before he left:
“I’m going to get you.”
Just after midnight, on October 10, 1991, Harris did just that.
A vicious spree
Dressing in a bullet-proof vest, black military fatigues, combat boots and a black, silk ninja-style hood, Harris armed himself with a nine millimetre Uzi machine gun, a .22 calibre handgun with a silencer, three hand grenades, some homemade bombs and a Samurai sword.
He wrote a two page letter alleging unfair treatment by the US Postal Service, and vowed to enact his revenge.
Booby trapping his door, Harris left his home and went after Ms Ott at her suburban apartment.
Harris forced entry to her home, and swung his sword towards her, deeply slashing her left shoulder and causing her to die.
He then made his way downstairs to where Ms Ott’s boyfriend Cornelius Kasten Junior was watching television, and fatally shot him behind the ear. But he wasn’t done yet.
At 2am, Harris made his way to the rear entrance of the Ridgewood post office where he shot and killed two mail handlers, Joseph Vander Paauw and Donald McNaught.
Harris then shot at a truck driver who had come to investigate his suspicious behaviour. The truck driver escaped unharmed, and alerted police.
Police attended the scene quite quickly, but were forced to retreat when Harris threw a homemade bomb at them.
However, after half an hour of negotiations, Harris gave himself up.
Trend of postal killings
Upon investigation, officers were able to pin him as the offender in a previous rape/murder case, where Harris sexually assaulted the wife and daughters of an investor who lost him money, before shooting the investor in his home.
Due to the emotion fuelling Harris’s spree killings, prosecutors attempted to argue that Harris was insane.
Nonetheless, he was sentenced to death row in 1992, dying in prison in 1996 of natural causes.
Harris’s murder spree is part of a slew of postal-related killings which have occurred throughout the United States since the 1970s, including the infamous Son of Sam shootings in New York City.
Most recently, on April 15 of this year, a previous Fed-ex employee performed a mass shooting at the Fed-ex Ground facility in Indianapolis, Indiana.
The gunman, Brandon Scott Hole, killed nine people and injured seven, before committing suicide.
Popular culture has noticed the trend as well, with many references to the phrase "going postal" in television shows and movies.
In the 1995 film Jumanji, character Van Pelt purchases a rifle at a gun store and the clerk asks him “you’re not a postal worker are you?”
In Brooklyn Nine-Nine, a US Postal Inspection Service agent comedically insists to the team that the term "going postal" refers to bringing goodness into people's lives.
And a video game series called Postal allows the player to take on the role of an insane mass murderer.
While "going postal" is a part of our usual lexicon these days, its sinister roots are truly disturbing.