Ever watch a wedding ceremony unfold between your good female friend and the jackass she’s inexplicably marrying? If so, you probably wanted to “speak now” — but instead, you held your peace. Forever.

Some couplings make you smack yourself in the forehead and think, “Why the hell is she with him?” Here, researchers attempt to answer that question.

The a–hole appeal

Jerks tend to possess a lot of characteristics that appeal to women, says Gregory Carter, PhD, a psychologist at the University of Durham in the UK. Those traits include a socially dominant and outgoing demeanor, lots of confidence, and vanity (i.e., a tendency to dress well and take care of themselves), Carter says.

And her attraction to such qualities could be biological. “All these [traits] signal to women that a man has confidence, good genes, and access to resources — things that from an evolutionary standpoint would have been appealing or offered security,” says Vinita Mehta, PhD, a Washington, DC-based clinical psychologist.

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Narcissists, psychopaths and Machiavellian types — or what psychologists sometimes call the “Dark Triad” cluster of negative personality traits — also tend to be very competitive, Carter says. They’ll chase women who are married, with another guy, or who are vulnerable — the types of girls “nice guys” wouldn’t hit on. That increases a creep’s access to potential mates, Carter says.

Attract women like a jerk

So how can you follow the prick’s playbook without becoming one? Men who talk about interesting goals or hobbies come off as confident, which women find attractive, says Sean Murphy, a researcher at Australia’s University of Queensland.

That doesn’t mean you should gloat about your six-figure salary or the epic hike you totally crushed last weekend. But elaborating on what you do or enjoy is a good way to play up your talents and achievements without seeming arrogant, Murphy says.

Humor and creativity signal to women that you have good genes, Mehta says. So if you do anything artsy — like take photos or play the guitar — mentioning those hobbies should raise your stock with women.

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Plus, the way you sit and gesture can signal whether you’re socially dominant or submissive, and dominance is a trait that women are programmed to love, Mehta says. Research shows you should spread your arms while seated and rest a hand on a buddy’s shoulder to give off that alpha-male vibe.