When Salomon Brothers bond trader John LeFevre received his first bonus on the job in 2002, he thought he’d save and invest the $75,000 windfall. That is, until he revealed his plans to his rabbi (that’s finance-speak for mentor).

His boss balked.

“ ‘Why the f - - k are you going to worry about trying to save money now? . . . Spend that cash,’ ” LeFevre recounts him saying in his new memoir, “Straight to Hell” (out July 14), which documents his years working on the Wall Street investment bank’s fixed-income desk. He dutifully complied, dropping his entire bonus in Saint-Tropez in five days.

“When you get into that world, they sort of mold you and shape you. And if you don’t embrace that culture, you’re not going to get promoted,” LeFevre tells The Post.

Like his fellow masters of the universe, LeFevre was soon consumed by excess — he got pleasured at lunch and crashed a brand-new cherry-red Maserati convertible a week after purchasing it drunk — during his years working in NYC, London and Hong Kong. He quickly learned the buddy-check system for bloody noses (midday cocaine sessions weren’t uncommon).

During one jaunt to Singapore, he even woke up in a hotel next to a prostitute, with no cash and no memory of how he ended up there, paying her $150 fee entirely with mini-bar provisions.

The tawdry tome is the follow-up to LeFevre’s infamous Twitter account, @GSElevator, which he started anonymously in 2011 to provide a satirical look at Goldman Sachs and banking’s general excess and bravado. It caused an uproar in the financial community. Tweets included “Every year, children learn a valuable life lesson: Santa loves rich kids more,” and “Each comma in your bank account adds an inch to your d–k.”

“It was about illuminating the soul and culture of banking,” LeFevre, now 36, tells The Post of @GSElevator, which boasts more than 700,000 followers.

“Goldman is typically held up as Public Enemy No. 1,” he says.

But to financiers, it’s the golden ticket.

“Goldman Sachs employees tend to be a little bit smarter, a little bit better, and that’s why people want to go there,” LeFevre writes. LeFevre, who grew up in Houston, Texas, was gunning for Wall Street ever since his high school days at the posh Connecticut boarding school Choate Rosemary Hall.

“The Wall Street dads [who visited] were the cool dads with sports cars and a propensity for profanity,” LeFevre writes in the book. “They’d tell our dean we were spending the weekend with them in Connecticut, only to let us disappear into New York City, where we’d take down a suite at the Waldorf Astoria and go to Scores and Au Bar.

“This is when I internalized the number one rule of life: ‘Rules are for the obedience of fools and the guidance of wise men.’ ”

His dreams came true when he joined Salomon Brothers immediately after graduating from Babson College in 2001. After a summer spent training in New York City, where he skipped lectures for a steady stream of Bloody Marys at Windows on the World atop the North Tower of the World Trade Center, LeFevre was placed in the firm’s London office.

He stayed there for three years, finally agreeing to move to Asia after his superior assured him that “chicks there love white dudes with cash.”

In 2004, LeFevre dumped his girlfriend (he bought her a pastry first, to lessen the blow, he writes) and moved across the world into the five-star Mandarin Oriental hotel.

It’s a whole different level in Hong Kong, where the maids perform oral sex, lunches are three hours long and include $300 bottles of wine, and white ex-pats basically get away with murder.

In the book, LeFevre recounts meeting with the head of hedge-fund sales at Salomon Brothers, “Dennis Lipton” (names in the book were changed), on his first day on the job there.

Lipton is on his way out of Hong Kong for a new gig in NYC and wants to introduce the newbie to his key clients before he leaves town.

After pounding drinks at the Shangri-La hotel for three hours and getting properly “lit,” LeFevre joins Lipton at a nondescript office building.

“Lipton is sitting on the couch. His pants are around his ankles. Some chick is on her knees, b–wing him. And another chick is standing on the couch, completely naked, with her knees slightly pressed against his shoulders,” LeFevre writes. “And there he is, our head of hedge-fund sales, who makes more than a million bucks a year, married with kids, sitting there, [with] some prostitute . . . ”

After they party, Lipton leaves him with the bill so his wife won’t see the receipt.

“When you get into that world, they sort of mold you and shape you. And if you don’t embrace that culture, you’re not going to get promoted.”

The frat-like atmosphere in banking is rampant, LeFevre says. So much so that schoolboy pranks are as integral to the job as one’s Bloomberg terminal.

During one dinner at an Italian restaraunt in Hong Kong’s Soho district, LeFevre and a table of raucous clients start a game where each time an individual goes to the bathroom, he has to return with something.

“So it started with a couple rolls of toilet paper . . . and then someone came back with a tissue box and a plunger, and it escalated and escalated and it culminated with me effectively getting a lifetime ban,” LeFevre tells The Post. (It’s one of three Hong Kong restaurants he’s been banned from over the years. LeFevre has also been permanently ousted from four bars, two hotels, and the private London club Milk & Honey.)

Often, women were the target of LeFevre and his colleagues’ antics.

“When I was in London there was a group of analysts who would make bets in the banking pool, and the loser would have to ask out the most unattractive female analyst the pool decided on to go out for dinner and a movie . . . it was a running joke,” LeFevre says.

But the former financier says he doesn’t regret his role in a locker-room culture that is undeniably disadvantageous to his female peers.

“And I never really thought of it like that because I was having so much fun at the time.” Plus, LeFevre says, “That was how you got promoted.”

#1: ‘Do what you love’ is great advice for making 30k a year. — GSElevator (@GSElevator) June 29, 2014

“I still remember the first time my boss told me a racist joke when I was a first-year analyst in London,” he recollects. “It was pretty offensive. But part of me was like, ‘Wow, I made it. He trusts me and is including me in this culture.’ ”

LeFevre admits that banking changed him. And not necessarily for the better.

“The first time I went home to Texas from Hong Kong, I guess I was rather flippant, dismissive with the waiter, and my sister looked at me and said, ‘Wow, you’ve become a bit of an ass—e.’ Each visit home, my mom would say, ‘Go to Walmart, walk around for 15 minutes, and re-acclimate yourself to the real world.’

#1: If your LinkedIn work history predates 1990 and you aren’t currently in a Porsche near a beach, why would I hire you? — GSElevator (@GSElevator) February 9, 2015

“In banking, you gradually sort of learn a new way of looking at honesty and fidelity, and your behavior shapes and shifts over time,” he says.

The business also started to shift. In 2007, the credit markets were going haywire, and LeFevre started thinking about making his exit. “It was just becoming so dysfunctional . . . there were just way, way more bad days than good.”

He left Salomon Brothers to do private equity in 2008, then a year later, joined a new boutique firm started by two of his former bosses.

In 2010, LeFevre was offered a job as head of debt syndicate in Asia at Goldman Sachs’ Hong Kong office, but the job offer fell through due to contractual issues. He spent the next year in Hong Kong, continuing to rage while working as a partner and adviser for a think tank startup. By the end of 2011, he was officially burnt out.

“I said, ‘This isn’t for me anymore. I’m just not that into it,’ ” LeFevre says.

He flew back to the States, bid farewell to his million-dollar salary, and settled down in Texas. He now lives in Woodlands, just north of Houston. He’s married to a 22-year-old he met at a bar, has two kids — a 6-month-old daughter and an 18-month-old son — and spends his days playing golf and writing. LeFevre says he hasn’t touched a drug since leaving Hong Kong.

“I don’t really have that many regrets,” he tells the Post. “There are some times when I could have been . . . less embracive of the culture. But everything leads you to where you are now. And I’m happy here.”