Gender, Sex Ed

Forbidden Fruit: How Many of Us Have Fantasized About Our Partner’s Best Friend? Or Their Sibling?

December 14, 2018 by Justin Lehmiller

In studying the sex fantasies of more than 4,000 Americans for my book Tell Me What You Want, I discovered that there’s one person who’s more likely to appear in our sexual fantasies than anyone else: a current romantic partner (or, if you’re single, an ex-partner). However, our fantasies aren’t only about our partners. For example, sometimes we fantasize about “forbidden fruit”—you know, people our partners might disapprove of, like their best friend or a sibling. Or perhaps we might fantasize about people that our culture or society would consider off-limits, such as someone else who’s married.

So just how common are these “forbidden fruit” fantasies ? And do they differ based on gender and/or sexual orientation? Here’s a look at what I found when I dug into the data:


As you can see in this table, fantasies about socially or culturally forbidden persons are far more common among men than they are among women, regardless of sexual orientation. Indeed, it’s striking just how similar heterosexual and non-heterosexual persons’ responses were.

Among men, about three-quarters had fantasized about sex with someone who is married, more than half had fantasized about their partner’s best friend, nearly half had fantasized about their best friend’s partner, and more than a third had fantasized about their partner’s sibling.

The numbers for women—and especially heterosexually identified women—were much, much lower. In fact, for straight women, less than half reported having any of these fantasies.

I included results for persons who identified outside the gender binary (these folks represented about 5% of the sample). Their responses were in between those of self-identified women and men, but tended to be a bit closer to women’s responses on average.

So how do we explain this pattern of results? It may have something to do with a finding I discuss in Tell Me What You Want, which is that men have more taboo sex fantasies in general than women. For some reason, men are just more turned on by the idea of doing things they’ve been told they can’t or shouldn’t do. This may stem—in part—from the fact that men tend to be higher in sensation-seeking tendencies, so perhaps they’re more drawn to taboos because it provides an extra thrill.

Alternatively, this may also have something to do with the fact that women are more likely than men to fantasize about passion, intimacy, and romance. Those emotions may be a bit more difficult to envision with forbidden targets, so perhaps that’s why women’s fantasies are even more likely to focus on their current partner compared to men.

Of course, other explanations are possible, too, and we need more research if we really want to understand what’s going on here. In the meantime, what these findings tell us is that forbidden fruit fantasies certainly aren’t rare—and, at least among men, they’re actually pretty common.

With all of that said, it’s important to note that having these fantasies doesn’t necessarily mean that people want or plan to act on them, or that they’re necessarily a sign of relationship dissatisfaction. Not all sexual fantasies are sexual desires. It’s also just human nature to be turned on by sexual novelty, such as by fantasizing about new partners and/or activities.

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Written by
Dr. Justin Lehmiller
Founder & Owner of Sex and Psychology

Dr. Justin Lehmiller is a social psychologist and Research Fellow at The Kinsey Institute. He runs the Sex and Psychology blog and podcast and is author of the popular book Tell Me What You Want. Dr. Lehmiller is an award-winning educator, and a prolific researcher who has published more than 50 academic works.

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