Kylie Jenner may have been wearing a classy “Eat Me Out” T-shirt, but at least she wasn’t at the theater. Small blessings, right?

Tell that to the slobs who turn up at Broadway shows dressed as though they’d just walked in from a tailgating party — one with a three-figure admission price, mind you.

When people were invited onstage at a recent performance of “Penn & Teller on Broadway,” many women looked as if they had stepped out of a jazzercise class, while men ambled around in hideous cargo shorts.

And it’s not just at the theater where folks have simply stopped trying: Offenders turn up at the Metropolitan Opera in Crocs. A colleague who used to work at the Neue Galerie — a museum housed in a former Vanderbilt mansion — would see visitors in cutoffs.

But high culture isn’t the only victim. At the airport, many fliers appear ready for bed in their saggy sweatpants — or even pajamas. Hot pants are maybe not the best idea at a gourmet restaurant.

And gentlemen, we know it’s hot and you’re exercising, but please keep your shirt on — or at least wear a tank top. Nobody wants to see your jiggly manboobs.

No wonder everybody from Patti LuPone on down is complaining that nobody knows how to behave anymore: If you dress like a child, chances are you’re going to act like one.

Partly this has to do with the visual erasure of style barriers. For every Kardashian trying too hard, you have a Steve Jobs wearing dad jeans and New Balance kicks 24/7.

It’s enough to make you long for the days when high-end restaurants had loaner ties and blazers for forgetful dudes, and you could be turned away from a club for a slack outfit. Style, low budget and comfort aren’t mutually exclusive. Keep that in mind if you’re older than 12.

Recently I had the opportunity to play at the West Side Tennis Club in Forest Hills, Queens. A longtime user of the city’s public courts and their anything-goes dress code, I complained at West Side daring to demand all white from its patrons — but I eventually caved because I badly wanted to try out the club’s famed grass courts.

And then it happened: There I was in head-to-toe white — everything bought at deep discounts online — and suddenly I wasn’t just playing tennis anymore. I was feeling special.

So while you can hold on to your crop tops and ratty band tees, you may also think twice about where and when you wear them. After all, if you dress better, you’ll feel better.