‘Float like a butterfly, sting like a bitch.”

That’s the motto brand-new “Real Housewives of New York” star Leah McSweeney swore by while filming her first season of the Bravo reality-show franchise, dropping April 2.

“Being on the show is like being in your primal state,” McSweeney exclusively told The Post between swings at Tribeca’s Trinity Boxing Club. “It’s like an animal kingdom — we’re all predators and prey.”

And while the single mom never actually came to blows with her fellow castmates — Luann de Lesseps, Dorinda Medley, Tinsley Mortimer, Ramona Singer and Sonja Morgan — she admits there was “a hazing process” when she joined the crew last September.

“They were like, ‘Whoa, who is this girl?’ I don’t really think they knew that much about me going in,” said McSweeney, who founded one of the first women’s-streetwear companies, Married to the Mob. “There’s this competitive aspect that we can’t help, just because it’s a show, and there’s a next season and [always the question of] who’s gonna be on it. That’s in the air, you know?”

When the Financial District dweller tried out for the series five months ago, she couldn’t picture herself lunching on the Upper East Side with the well-to-do “RHONY” queen bees.

“After [producers] first interviewed me, I was like, ‘They’re never going to pick me,’ ” laughed McSweeney, 37. “I literally said, ‘I’m anti-socialite.’ But, I guess they liked that.”

A few weeks later, the designer learned she had made the cut.

“I was terrified and so happy at the same time,” she said.

Besides Mortimer — whom McSweeney met through mutual friends — she had never crossed paths with the other ladies.

Once filming got going, she said, “the most interesting dynamic” was between herself and Singer, who has earned the nickname “Singer Stinger” for her biting ­insults.

“You have to understand, my mother is only a couple years older than her,” McSweeney explained of the 63-year-old Singer. “I was going through some issues with my mom during the show, which everybody will see, and I think that my emotional outburst with Ramona had to do with a lot of my own issues with my mom.

“Ramona took me under her wing. She took a liking to me right away, but she also, I felt, was hard on me and holds me to a different expectation,” she added. “Maybe she sees [in me] herself when she was younger?”

On the other hand, de Lesseps surprised her the most. “I didn’t see me and her like really getting that close, but she’s f–king amazing,” said McSweeney.

And even though the new leading lady was put through the wringer a few times, she quickly learned how to roll with the punches.

“I had a very rough all-cast trip and I think after that I was like, ‘You know what? Everyone just saw me be insecure and upset,’” she said, foreshadowing what is sure to be a buzzed-about episode. “So there’s nothing really left to fear after that.”

McSweeney’s empowered attitude certainly made an impression on Medley, who recently revealed in an interview: “I thought that I was the badass in town when I joined the show, but I think [McSweeney] puts me to shame.”

It’s a reputation that’s stuck with the designer ever since she was a teen growing up in Chelsea. McSweeney attended the Upper East Side’s elite Convent of the Sacred Heart Catholic all-girls school — until she was expelled at 14 years old.

“Honestly it was total bulls–t,” she said. “They made me the scapegoat and said I was a bad influence on the class.”

With that, McSweeney was whisked away to Newtown, Connecticut, by her mom, who works as a social worker and therapist, and her dad, a retired city health inspector.

After high school, she moved back to the Big Apple and attended the Fashion Institute of Technology for a month before dropping out to focus on starting her own business.

“At that time, there was no streetwear for women at all,” said Mc­Sweeney, who was influenced by the underground hip-hop scene. “I was wearing guys’ stuff and tying it up or cutting it up or whatever.” After meeting her now-ex Rob Cristofaro — the two have a 12-year-old daughter, Kier — and working for his streetwear company Alife, she decided to strike out on her own in 2004.

She had a unique source of funding. In 2002, during an altercation at the Hammerstein Ballroom, two NYPD officers allegedly smashed McSweeney’s face into a subway grating, knocking out two teeth and netting her a $75,000 payout that helped kick-start her dream.

McSweeney’s line is often printed with phrases like “Supreme Bitch” and “Face It You Basic.” She’s collaborated with German luxury brand MCM and her clothes have been worn by Rihanna, Cara Delevingne and McSweeney’s icon, Lil’ Kim. She also counts controversial writer Cat Marnell as a close friend.

She and Cristofaro split in 2008, and McSweeney is now single with a message for interested men: “My DM’s are open.”

And the new Housewife, who hosts the podcast “Improper Etiquette” focused on women’s issues, hopes that the season premiere of “RHONY” can bring some levity in this age of chaos and anxiety.

“My heart is f–king broken for New York right now,” she said of the coronavirus pandemic. “If [the show] can bring comic relief, and I think it will, then that’s great.”

Photos: Annie Wermiel/NY Post; Stylist: Nicole Zane; Hair: Jackie Fanara; Makeup: Natalia Carrasco; Stylist Assistant: Haley Wells; Location: Trinity Boxing Club, 116 Duane St.