Hours before a date with a Tinder match, she texts, “I hope you’re not offended, but how do you identify sexually? Have you been in a relationship with a woman?”

Was I offended? Not really. But disappointed? Absolutely.

What might normally be considered rude has become, I’ve noticed, downright de rigueur — because I’m a bisexual woman.

Fear or hatred of bisexuals, biphobia, as it’s called, is surprisingly, flagrantly robust in the land of rainbow flags. While there might be a considerable number of women looking for women here, many lesbians aren’t shy about treating bi women with skepticism, distrust or rejection. We’re seen as not “gay enough,” simply because we aren’t attracted solely to women. (Bisexual men, I am told, also face a host of complications.)

Twice on a first date, I’ve been told, “I don’t date bi girls — I just sleep with them.” Then there’s, “How many people have you slept with?” or its more presumptuous cousin, “Have you ever been with a woman?”

One woman I dated was insistent that I call myself a lesbian. I refused.

“Constant denial of a group’s existence makes it hard to exist,” said Allegra Hirschman, who is on the board of directors of the Bay Area Bisexual Network.

But we do exist. A 2010 study in the Journal of Sexual Medicine found that 3.6 percent of U.S. women identified as bisexual, while 0.9 percent identified as gay or lesbian; a 2007 survey of lesbian, gay and bisexual people by the City University of New York found that more than half — 65 percent — identified as bisexual, compared to 35 percent as gay or lesbian.

Activists worldwide have begun marking Sept. 23 as an occasion to speak out about bisexual visibility. Berkeley, in 2012, became the first city to officially recognize Bisexual Pride Day. In Hollywood, high-profile women have increasingly spoken about their non-monosexuality, including Miley Cyrus, Amber Heard, Kristen Stewart and Evan Rachel Wood.

Even Robyn Exton, who founded the female dating app Her, has to justify her sexuality. She has been told “I f— hate bisexuals,” to her face, and faced derision at events such as Palm Springs’ Club Skirts Dinah Shore Weekend, often called “lesbian spring break.”

Imagine if another descriptor — say, skin color or body weight — prompted such explicit disdain.

“I’m so used to it,” Exton said.

The justifications follow a common refrain: Many are worried that straight-looking bisexual women are really just “bi-curious.” Some have been heartbroken by bi women who “go back to men” after a breakup. For San Francisco lesbian Zena Ah Chin, that’s happened more than once, and an ex-girlfriend told her that dating men was just easier.

In a June 2017 study from American University, assistant professor Ethan Mereish confirmed that bisexual people experience unique stigmas and hostility, including the perception that their orientation is unstable or that they are disloyal.

“They assume we are dishonest, confused, incapable of fidelity, selfish and greedy,” Hirschman said. “The idea that bi women will end up with a heterosexual cis man holds ground statistically, but that is simply a numbers game as there are more men who fit this profile than women who date women.”

Carol Queen, staff sexologist at retailer Good Vibrations and founder of the Center for Sex & Culture, has been battling the stigma for more than 40 years. When she came out as bisexual in the ’70s, the LGBT community treated it as a phase, she said. “It was the fence-sitter rhetoric, a bi epithet that, ‘You don’t know where you are going to wind up, so it wouldn’t be good to have a relationship with you because you can’t be trusted,’” Queen said. At one time, she called herself a lesbian to get a girlfriend.

That stereotype has been undercut by a 10-year study by University of Utah psychologist Lisa M. Diamond, who found that bisexuality among women is a stable identity rather than a transitional phase toward lesbianism.

Still, it’s not hard to see how one might associate an ex’s bi-ness with heartbreak, in the same way that one might swear off a proverbial Latin lover or someone younger than a certain threshold.

Lesbian matchmaker and psychologist Frankie Bashan asks clients if they are open to dating bi women in part to educate women that bisexuals aren’t entertaining themselves before they “find a man.” Bashan has seen clients “write off” bisexual women based on one bad experience. “These bad experiences get overgeneralized and therefore become barriers. When we explore their fears, they’re not really based on any facts,” she said.

When bi women advocate for bisexual acceptance, it isn’t just bellyaching about dating. A 2015 study published in the Journal of Public Health found that bisexual women were 64 percent more likely to report an eating problem and 37 percent more likely to commit self-harm than lesbians.

This is due in part to loneliness — from what Mereish calls “double discrimination,” meaning stigma from both side of the gay-straight divide, coupled with a relative lack of research on the specific effects of bisexuality on health.

Ultimately, I have resisted the temptation to sink into a simpler “gay” or “straight” descriptor, and have been lucky to date people who understand that if I’m attracted to them, that’s enough.

And to the woman who asked about how I identify, I answered, “I identify as ‘sexual,’ but since I just got out of a relationship with a woman, let’s just meet each other first, shall we?”

Maghan McDowell is a Peninsula freelance writer. Email: style@sfchronicle.com