If there’s one thing those millennials don’t know how to do, it’s be adults. They turned “adulting” into a verb, and they are inept in its practice.

We’ve read all those eye-opening pieces on how they don’t know how to use stamps or register to vote. We’ve poked fun, had a laugh, exclaimed, “Kids these days!” Now it’s time to actually do something about it.

We’re talking about a generation of people, and the generations behind them, who simply lack sufficient knowledge to get by in the adult world. We need to bring back practical classes in our public schools that will teach key life skills.

Kids used to take often mandatory classes, like shop and home economics, where they learned woodwork and cooking. It wasn’t considered condescending to teach them these basic skills, which allowed them to function as more competent adults outside of school.

Perhaps previous generations were able to adult better because their parents and teachers took the time to show them how to do it.

Along with acquiring practical knowledge, young people today need courses that include a social component. Millennials and their successors have no real social skills because they have limited social interactions. Social media has made people so withdrawn from others that a recent study had a full 20 percent of millennials reporting that they have no friends at all.

They’re the first generation that grew up on the Internet, it makes sense that their social skills aren’t what they should be. We tsk-tsk them while staring down at our phones but should be teaching them some lessons about how to relate to others instead.

Kathleen McKinley, a writer in Texas, told me, “My son’s girlfriend’s mom died. She posted and texted the address of the funeral home to her friends. It was in another state, so they all texted or messaged back, ‘So sorry! I can’t make it.’ It didn’t seem to occur to any of them the address was for sending flowers. As it ended up, only Boomers sent flowers.”

Young people grew up clicking “like” to send a message of support or posting a sad-face emoji to convey condolences. They have no idea how inappropriate that is and that more is needed in such a situation.

People used to take etiquette classes, sometimes at their school, to teach them table manners and how to answer the phone. Times have changed, and it’s less important now to know which fork to use at dinner, of course, and few people share telephones these days, but teaching kids how to behave in society and cooperate with others is still necessary, indeed more so.

A National Public Radio piece last year on the rise of Family and Consumer Sciences classes noted: “FCS classes also commonly address personal finance, healthy relationships, how to balance work and home responsibility, and child development. ‘In the good old days you got that at home,’ says Megan Vincent, a FCS education specialist for the state of Montana. ‘But now you have two working parents . . . these courses fill the gaps for what parents can no longer do.’ ”

Which, often, is the real reason young people can’t manage healthy adulthood: No one is at home to teach them how to do it.

That is not necessarily meant as a criticism of households with two working parents, but as an explanation of why younger people are having such a hard time functioning in adult society. Better to stop mocking their café-bought avocado-toast habits and teach them how to make their own avocado toast at home instead.

Good news? Some schools are catching on. In Indiana and Pennsylvania, schools require FCS coursework to graduate. A Life 101 class offered at an Indiana high school teaches kids how to dress for job interviews and how to follow-up after submitting an online resume.

One employer told me she had a millenial seeking a job ask to postpone an employment interview with her because she would have to skip her Zumba class. Teaching millennials not to overshare should be part of the course.

The generation that spends their lives online needs to know that not everyone needs to know everything. And don’t cancel a job interview over a Zumba class.

Kids these days!

Twitter: @Karol