Two years ago, Abby Norman was in the heat of the moment with a guy she was casually dating. He didn’t have a condom — and the one she had on hand was expired.

Norman, now 25, was raised to be diligent about reproductive health, so she didn’t think twice asking about her partner’s sexual history: How many partners did he have? When was the last time he was exposed to a sexually transmitted infection (STI)? Does he always use a condom?

“He was very shocked at how direct I was, and I don’t think a woman’s been that direct with him,” Norman, a writer who lives in Camden, Maine, tells The Post. Her partner hesitated to answer her questions, and that made her nervous. Unfortunately, Norman says, this isn’t the first time people have been put off by her concern for her own sexual health.

“I’ve gotten teased by my partners and my peers, and my diligence has been seen as being a bit intense,” Norman says. “I feel like there’s a culture of ‘chill,’ or not wanting to be perceived as intense.”

Her friends aren’t the only ones who are cavalier about their sexual health. A new report from the Centers for Disease Control and Prevention found a recent spike in STIs such as chlamydia (up nearly 6 percent since 2014), gonorrhea (up nearly 13 percent) and syphilis (up 19 percent) among young people. The CDC says that almost 20 million new STIs occur every year, over half of them afflicting people between the ages of 15 and 24.

The reason millennials are catching STIs quicker than they catch Pokémon? Many are simply not using condoms.

“We are definitely seeing young people who don’t practice safe sex,” says Dr. Hansa Bhargava, a WebMD medical editor and pediatrician based in Atlanta. “In a casual relationship, if a person feels like they ‘know’ the other person, they are less likely to practice protected sex,” she says, referring to the “friends with benefits” phenomenon.

A 2015 CDC study found that condom use among sexually active high schoolers dropped from 63 percent in 2003 to 57 percent in 2015. A study that same year by Skyn condoms found that 48 percent of millennials use condoms “never” or “rarely.”

“They’re really constricting,” says Nick, a 31-year-old content manager based in Brooklyn, who hates condoms and rarely wears them because they don’t feel good.

“All of them seem to fit differently, it doesn’t really feel organic, and they’re just generally unsexy,” adds Nick, who asked not to disclose his last name for professional reasons.

Nick says that while he obliges when his partners ask him to use protection, a few women actually prefer to go without it.

“I start putting a condom on and the girl suggests I don’t use one — but that happens rarely,” he says.

Psychotherapist and sexologist Eric Garrison says he’s seen a “noticeable increase” in STIs among young people in the past 10 years, and attributes it to the popularity of social media.

“Sex is easier to do than to talk about, and the style of communication [for young people] is texting and short messages where you’re tweeting this and tweeting about that, but talking about an STI is more than 140 characters,” Garrison tells The Post. “Young people just don’t have those communication skills.”

Other millennials say they’re aware of the risks associated with unsafe sex, but that they sometimes forget that their chosen form of protection doesn’t prevent all STIs.

Gay men such as Ben, a 29-year-old designer based in Hell’s Kitchen, say the rise of PrEP — a pill that helps prevent HIV infection — coupled with the fact that young gay men didn’t live through the AIDS epidemic of the ’80s, has made his peers more nonchalant about STIs and less inclined to use condoms.

Similarly, women sometimes believe that because they’ve received the human papillomavirus (HPV) vaccine, they too are less at risk.

“There’s a kind of [mindset] that PrEP protects you from HIV, and other [STIs] are curable,” says Ben, who didn’t want to use his last name for professional reasons. “I feel like a lot of gays here don’t use condoms . . . even though that’s not my thing.”

For heterosexual couples, the fear of unintended pregnancy often outweighs the fear of STIs, leading them to opt for forms of protection that guard against the former but not the latter.

Lea, a 25-year-old beautician who contracted chlamydia from her high school friend in 2014 after having unprotected sex, says that because she was on birth control and she knew her partner, she didn’t feel like she was at risk for an STI.

“I’m a trusting person. I knew him and I usually never asked guys [their sexual history] before, because [I assumed] if someone was aware of it, they’d have it taken care of or they’d tell you,” Lea, who didn’t disclose her last name for reasons of privacy, tells The Post.

After her STI scare, Lea says she was abstinent for seven months.

“To me it was a wake-up call to be more proactive and not be so willy-nilly about [using protection].”

To make matters worse, STIs are becoming more resistant to treatment: