Mommies, meet your worst nightmare.

She blasted an online debate on how to properly pronounce a baby’s name with the comment, “Give her a name that can’t be altered, like Jennifer. Otherwise Shut The F–k Up.”

When a mom posted a picture of her baby in a onesie that read,“$5 Footlong” with an arrow to his crotch, she wrote, “Since when did it become acceptable to compare a baby’s genitals to a sub sandwich?”

Now The Post can reveal that the anonymous woman behind the scathing blog STFU, Parents is Brooklyn writer Blair Koenig.

Koenig is 30, has a long-term live-in boyfriend, two cats, a tattoo — but no kids. She started the brutally snarky site in 2009, she says, to out parents who incessantly post outrageous, tasteless and self-absorbed photos and updates bragging about their kids on the Internet.

The site’s tagline speaks for itself: “You used to be fun. Now you have a baby.”

In response to a parent posting a photo of a child with hair full of poop, Koenig wrote, “Seriously, who posts a picture of the crap on Facebook and then writes, ‘LOL, yea but it was funny’? Is nothing sacred anymore?”

A dad put a photo on Reddit of his 3-year-old wearing a so called “shaming sign” saying: “I pooped in the shower and daddy had to clean it up. I hereby sign this as permission to use [the photo] in my yearbook senior year.” In response, Koenig wrote: “She looks so damn happy.”

Koenig categorizes her blog entries along these lines: Sanctimommy — the better mom than you moms; Woe is Mom — the non-sleeping martyr moms; Mommy Jacking — the every thought turns back to my child moms; and Gross Out Factor — devoted to the too-much-information-providing parents.

As the site’s fan base grew, Koenig’s inbox filled with readers’ wacky examples of online posts from all over the country. Those were followed by angry e-mails from offended and rattled parents and what she calls a death threat.

“I don’t like it. It’s a gang mentality, and I feel bad for the people [whose posts are featured],” said mom-of-two Cherie Corso, of Pelham. “They become victims and a target of ridicule. I think the site is mean-spirited.”

Not a parent herself, Koenig faces questions of jealousy or bitterness. “I am absolutely not bitter. I love children. I would like to have children one day. For me, they are part of my near-future, not my present. I have not yet tried to have children, and I’m not yet married,” she told The Post.

“It’s meant to be a humorous site. Most of all, it’s meant to be more of a cultural observation than a really hard-line criticism.”

Jennifer Diel, of Merrick, LI, defends her habit of sharing kid news online.

“Every mom thinks their kid is the smartest and most beautiful child in the world. If someone doesn’t want to look at my photos,then God bless them, block me” on Facebook, she said.

Anesthesiologist Nicky Lotherington, 44, a mom-of-one from Park Slope reads STFU, Parents every day.

“It makes me laugh out loud all the time. I hate the way we all become so incredibly infatuated with our children. We lose all sense of reality,” she says.

“People are always using Facebook to brag about their kids, and I’ve unfriended some of them so I don’t have to look at the crap they post!”

“It’s not for everyone, especially if you don’t have the same sense of humor as my followers,” admits Koenig, whose site now gets around 1.5 million page views every month and has paid advertising.

“I actually think I am providing a public service.”

Koenig says she has received thank you e-mails from people frustrated by their “mombie” friends whom they tactfully direct to her blog in an attempt to get them to mend their ways.

Anonymity protected Koenig, a Fort Greene resident, for years. As the blogosphere speculated about her identity, only a small group of friends and family have known that the subversive site is her brainchild.

Koenig, who is from Atlanta, studied journalism and film and took a job in marketing when she moved to the city seven years ago, but left it to start the blog.

Once it got noticed, she signed a deal with Perigee, a division of Penguin, to write a book based on the blog, to be called “STFU, Parents: A Guide to the Jaw-Dropping, Self-Indulgent, and Occasionally Rage-Inducing World of Parent Overshare.”

The book is due out in April.

The book made it impossible for Koenig to remain anonymous — she’ll appear on “The Ricki Lake Show” today. But she is reticent.

“I’m a little nervous,” she says, smiling at the irony. “Because I’m a private person.”

PRE-ORDER “STFU, PARENTS: A GUIDE TO THE JAW-DROPPING, SELF-INDULGENT, AND OCCASIONALLY RAGE-INDUCING WORLD OF PARENT OVERSHARE” HERE