“Read my lips: I don’t care. It’s an irrelevancy,” Mayor Bill de Blasio declared Wednesday.

Well, that’s a little cold.

De Blasio is back in the deep weeds, his minions having booted vagrants from a couple of Brooklyn subway stations so the bums wouldn’t spoil a weekend campaign photo op.

And getting caught at it.

And then lying about it.

And then getting caught in the lie, which clearly has made the mayor a tad peevish. This is understandable, because the episode exposes him as a man who can’t even stage a four-subway-stop publicity stunt — even as he runs for a second term as chief executive of the world’s greatest city.

(God surely must love New York, given the people it manages to survive.)

De Blasio had set out Sunday to throw shade on Gov. Andrew Cuomo and his torturous transit system — a noble cause, actually. The governor needs all the subway grief that can be heaped on him.

And what better way for de Blasio to do that than by hopping an F train from his Park Slope gym to his new campaign headquarters in downtown Brooklyn.

No scruffy people allowed, though. Bad optics.

“Before the mayor arrives at the 4th Avenue station, [police] officers are to sweep the station for homeless persons as well as the Jay Street station,” reads an NYPD email obtained by this newspaper — to the extreme discomfort of the mayor, his Three Stooges press shop and its deputy director, Eric Phillips.

Phillips opened with a high-dudgeon denial that the bum-sweep order had ever been given. Then, confronted with the email pretty conclusively demonstrating otherwise, he stuck by his story — hinting darkly that the email itself was a fake.

As if.

Anyway, here are some things Phillips obviously didn’t learn in press-secretary school:

Don’t let your principal do dumb things.

If he insists, and he gets caught, never lie about it — unless you’re certain you can get away with it.

But if there’s a paper trail, you almost surely won’t get away with it.

The mayor and his A Team broke all those rules: They did a dumb thing; they lied, and then they got caught.

So once again New Yorkers are reminded that they are governed by dumb liars. Not a news flash, of course.

Yet what does it all mean?

For one thing, it’s not an irrelevancy. Far from it.

Yes, the practical consequences likely will be slight — de Blasio is running for re-election virtually unopposed, save for a smart but vastly underfunded, outgunned and unknown Republican assemblywoman from Staten Island.

But did you know that city Comptroller Scott Stringer has never audited the NYPD’s CompStat program — the repository of the data City Hall regularly cites to support claims that New York is the Safest Big City In America™?

Maybe that’s true (even if growing street chaos suggests otherwise), but without an audit, nobody knows for sure — and what serious person would take de Blasio’s word for it?

Similarly, City Hall says it has added thousands of “affordable” apartments to the city’s housing base — but has it? Has anybody actually counted them? Should the claim be taken purely at face value?

And what about pre-K? The mayor’s signature program has been an undisputed boon to the teachers’ union and the city’s politically, um, grateful not-for-profit sector — but how many kids have been helped (apart from the free day-care)?

Plenty, says City Hall. But — again — why should anybody believe City Hall? Especially now, given de Blasio’s obdurate hyperventilating on BumSweepGate?

And it’s not just that: The de Blasio administration has lied about everything from Lower East Side nursing-home conversions to the city’s surging and increasingly aggressive street population to Central Park carriage horses to deteriorating public school performance to campaign finance violations to . . . well, the list is virtually endless.

The mayor and his teammates aren’t terribly good liars — for real expertise in that field, one need go north to Albany — but that’s not for lack of trying. No lie is too small not to be told — and then compounded.

Thus has Bill de Blasio forfeited the trust handed him by New Yorkers three-plus years ago. And that’s far from irrelevant. It’s pitiable.

Bob McManus is a contributing editor to the Manhattan Institute’s City Journal.