I went on my first trip aboard a superyacht. I learned from my etiquette mistakes and fashion crimes the hard way.

From the moment I stepped aboard my first yacht — no, actually from the moment I stepped off the sidewalk onto the gangplank to get to the yacht — I’d already outed myself as a novice. “Shoes!

Shoes!” one of the hosts called out.

I’d made the cardinal sin of keeping them on instead of removing them before even touching the boat. (Yachts, I’d later learn, tend to have delicate exteriors and a dedication to squeaky-clean interiors.

As such, they’re typically shoe-free zones.

So much for half the contents of my suitcase.) The blunder would not be the last time I unintentionally made it painfully obvious that I was not, in fact, the type of ultra-high net worth individual who typically vacations on this 176-foot, four-deck, six-bedroom Greek superyacht named Persefoni.

That honor is more often reserved for stars like Brad Pitt, who was reported to sail aboard it — I mean “her”— while filming his upcoming film, “The Riders.” But Brad Pitt I am not.

A freelance writer in Brooklyn I am.

My yacht is “The People’s Yacht,” aka the $4.50-for-one-way NYC Ferry.

It was only through a lucky set of connections and circumstances that I got invited to join a handful of writers and creators aboard the Mediterranean marine craft in May.

Most were European; all were industry veterans.

While I said things like “rope” instead of “line,” they talked in knots and flybridges, and swapped stories from extravagant boat shows in destinations like Monaco and Cannes.

In other words: Everyone else instinctively slipped off their shoes before stepping aboard.

Here’s what else I learned about superyacht life the “hard” way.

After receiving the grand tour of Persefoni — hot latte in hand, since the chief stewardess insisted I couldn’t possibly want “just a coffee” — I reached out to take my roller bag to my room.

The crew intercepted so swiftly you’d have thought I was reaching for a hot stove instead.

Turns out, guests aren’t supposed to haul their own bags — not only because that kind of manual labor is below most billionaires, but also because non-crew members can’t be trusted to keep the interior un-scuffed as they go about their clumsy ways.

Maybe this level of service is to be expected, given that chartering this yacht for a week typically costs more than $200,000 — not even counting expenses like food, drink, and fuel.

After that, the only finger I lifted was to push a service button.

That’s right: Discreet controls adorned various tables and walls; push one if you’d like a cappuccino, a carafe of Champagne, a coconut water.

Look, I’ve seen “Below Deck.” I know fine dining for “discerning” eaters is a part of the yacht-life package.

Still, I wasn’t prepared for both the quantity and highly customized quality of each multicourse meal that Persefoni’s chef — who’s rumored to have cooked for A-plus-listers and at least one president of the United States — prepared.

The team rolled out plates of charred octopus, grilled halloumi, fresh gazpacho, and smoked eel.

Warm pita and prawns preceded spaghetti aglio e olio eaten al fresco one afternoon.

There were cakes piled high with berries and whipped cream at breakfast; chocolate lava cake and tiramisu after lunch.

All this despite the fact that one guest had celiac disease, one couldn’t stomach red meat, and one hated onions.

I wasn’t a saint either: I don’t really like fish.

Bless Chef Sotiris, who took it all in stride.

By the time our party was ready for dinner the first night, it was close to 10 p.m.

I was nearing delirium, having been on a 10-hour international flight and awake for nearly 24 hours.

Alas, jet lag is no excuse for my sartorial choice: I wore, I regret to inform you, jorts.

And not a tailored, dark-denim variety.

Nope, these were cut-offs more appropriate for mowing a Midwestern lawn than sailing a Mediterranean Sea.

The other women, by contrast, arrived in colorful sundresses, curled tresses, and thoughtful jewelry.

When one saw me, she playfully chided: “Well, that’s a first!” It was also a last.

I only packed a carry-on-sized bag, and still, most of its contents went unused.

In addition to the strappy heels, flip-flops, sneakers, and slip-on Toms that had no business being on board, I’d packed toiletries like shampoo, conditioner, and lotion.

I was imagining the kind of spare bathroom I’d come across on cruises and a catamaran, where the toilet may as well be in the shower, and the only personal-care products you get are the ones you pack.

This was a superyacht — the type that has 13 crew members for a maximum of 12 guests and where, the second you step out of your room for that first iced frappe, someone sweeps in to draw the curtains, refresh the towels, and tidy up the bedding.

Needless to say, not only was my shower large enough to include a stone step to sit or shave a leg upon, but it also included soap, shampoo, conditioner, and natural loofahs derived from sponges of the sea.

Before the trip, I had one first-world worry: Would I be able to exercise?

I had a triathlon coming up a few weeks after the trip, and regardless of my training schedule, I am not fun to be around if I haven’t started my day with at least a little sweat.

Add to that the thrice-daily, sit-down, multi-course meals, and I feared I’d be bloated and cranky despite my luck. (Which in turn would make me feel guilty for not just being grateful, too.) I needn’t have fretted: Persefoni’s top deck was outfitted with weights, a treadmill, a spin bike, and a Tonal machine.

And when I jumped into the sea for an open-water swim, a crew member followed, unprompted, on a Jet Ski.

When I emerged, Captain George called me a “hero” — apparently, the crew agreed that braving 68-degree-Fahrenheit water wasn’t for the faint of heart.

Perhaps they were buttering me up, but I took the compliment.

I also took away a yacht-life lesson: The whole point is to do what you want.

Just don’t wear shoes (or jorts) along the way.