The jealousy between various government entities is the stuff of legend, like excuses as to why nobody figured out that terrorists were here learning to fly planes into very tall buildings. But usually, that plays out between law enforcement agencies. At least they all have guns. The mailman, on the other hand, is easy game.

Late in the afternoon on St. Patrick’s Day, Glen Grays, a 27-year-old African-American mail carrier, was making his rounds in Crown Heights, in Brooklyn, about to leave a package at 999 President Street.

Just in case you are unaware, Crown Heights is not one of those neighborhoods in Brooklyn where hipsters live.

On this afternoon, Mr. Grays was descending the steps of his mail truck backward, as postal workers often do to minimize wear and tear on the knees, when out of the corner of his eye he noticed a car making a sharp right turn onto President from Franklin Avenue. Mr. Grays shouted at the driver, climbing back up the steps to avoid getting sideswiped. The black car, in Mr. Grays’s telling, came tearing back his way in reverse. The driver said to him, Mr. Grays recounted, “I have the right of way because I’m law enforcement.” The unmarked car held four plainclothes police officers, according to the Brooklyn borough president’s office, which has taken an interest in the case.

One might suppose that this unmarked black car carrying four plainclothes police officers must have been responding to something very serious to be driving so recklessly as to nearly sideswipe a mail truck. But whatever emergency demanded such a response, it was nothing compared to these cops’ need to deal with this insolent mailman.

By the time Mr. Grays arrived at the front door of 999 President Street, the police were approaching him. A video of the incident, taken by an observer on the street, begins at this point and shows Mr. Grays, in his postal uniform, as he is handcuffed, frisked and taken to the unmarked car. The officers tell him to stop resisting, even though there is no evidence in the video of resistance.

But that’s just what happened on the street, because what happened afterward was in the backseat of the unmarked car, where video failed to see.

What the video does not show, Mr. Grays said, is what happened next, after he was placed in the back seat of the unmarked car, with his hands cuffed and without a seatbelt, compelling him to leave the mail truck unattended. The driver, who had turned around to taunt him, hit the vehicle in front of them, Mr. Grays said, causing him to bang his shoulder against the front seat. Mr. Grays was then taken to the 71st Precinct station, where he was issued a summons for disorderly conduct that will require him to appear in court. He was then released.

Note that little detail, that by arresting the mailman, they left “the mail truck unattended.”  And you thought they didn’t send the check, right?  No, it’s not nearly as stupid as the Tennessee imbecile, Tyrel Lorenz, who leapt into the back of a pickup, leaving two arrested persons to wander away, as he killed the driver of the speeding bullet, but still.

And to add a note of irony, because stupid, hostile and arrogant is no longer good enough to make a story worth reading:

Mr. Grays’s fiancée is also shaken. She is a New York City police officer he met while delivering the mail.

Some days, the mailman rings twice. Others, not at all, because he’s been arrested and taken to the precinct so he can be given a summons.  And the Brooklyn borough president, who was also a cop, took notice of his constituents’ failure to get timely delivery of their mail.

On Tuesday, the Brooklyn borough president, Eric L. Adams, himself a former police officer, released the video at a news conference, expressing what he said was his outrage over the ostensible violations of the civil rights of yet another young black man, this one an employee of the federal government.

This, of course, made Mayor Bill de Blasio sad, so he too took notice.

About Mr. Grays’s encounter, the Police Department said only that the matter was “under internal review,” in an email response to queries. Mayor Bill de Blasio’s deputy press secretary, Monica Klein, added that the mayor would be “in close touch with Commissioner Bratton over this incident’s investigations and findings.” (William J. Bratton is the police commissioner.)

There’s gonna be some hell to pay here. No, not for the cops, who will have reasonably feared this vicious federal postal worker’s reaction to their protecting and serving the residents of President Street. After all, it’s well-known amongst cops that mailmen go postal, and some have even been known to carry knives.

But for Glen Grays, there will be repercussions, as the worst thing a mailman can do is leave his truck unattended.  People could steal things from an open USPS truck, and postal workers have a sworn duty to make sure the mail gets delivered.  It’s outrageous that Grays let the mail-receiving people of Crown Heights down. If only there were cops around to protect them.