(NEXSTAR) – Few things are as universally reviled as a loud phone conversation infringing on your personal space. (Mosquitoes and taxes aside.) Doing it on loudspeaker is even more incendiary.

To me, having a phone conversation on speakerphone in public is puzzling. Doesn’t it make it harder to hear for everyone involved? Yet in the past month I’ve seen this behavior play out in a crowded airport terminal, the lobby of a boutique fitness studio and the grocery store pasta aisle. (Nowhere is safe!)

Aside from being odd, it’s rude, say etiquette experts. “Taking a call on a loudspeaker around others can unintentionally send the message that you’re not considering their presence or personal space,” said Myka Meier, founder of Beaumont Etiquette. “It can come across as inconsiderate or even self-centered, as though you assume everyone else should be subjected to your conversation.”

The fact that it’s a phone conversation — not just in-person chit-chat — could be part of the reason people find loud speakerphone calls so grating, speculated Ozlem Ayduk, professor and chair of the UC Berkeley psychology department. Because people have another choice (using headphones, or waiting until they get off the hypothetical bus), it seems like an intentional affront to other people’s peace and quiet.

“Talking to someone out loud in person on a bus where you’re dominating everybody else’s consciousness is just as rude as talking on the phone … in terms of real impact, it’s the same,” Ayduk said. “But there’s something about it being a phone, because I think we have conceptions that phone conversations are private, so it’s violating that expectation or assumption.”

People who use hearing aids (and might experience feedback when they hold a phone up to their ear) may get a free pass, but they’re not the only ones transgressing this unspoken rule.

The motivations for those without hearing impairment isn’t clearcut. It could be a number of things that lead to people speaking loudly — on the phone or otherwise — with abandon.

“I have no idea, but the person talking on the phone on a bus could be like, I don’t give a damn about all these people, you know, they’re just strangers to me. I’m never going to meet them again,” Ayduk said. “There may be some more nefarious reasons like somebody is narcissistic and they want to show the world how many friends they have. It could be totally benign to nefarious.”

They may also have trouble reading social cues and may not realize how their behavior impacts others, she explained.

Plus, how we act in any social situation also depends on the context we grew up in, our individual values and our goals. What’s rude to one person could be completely fine to another.

“We tend to temper our behavior depending on how we think it’s perceived, how socially acceptable those behaviors are,” Ayduk said.

The more you see the behavior happening around you, the more normalized it becomes. So if you see people speaking loudly on the phone all the time, you may not shy away from doing it yourself.

“Humans learn from observing other people’s behaviors. And especially in situations where there may not be very strong established norms, they look to others to gauge their own behavior,” she said.

Meier, for her part, hopes the norms around loud phone conversations won’t change too much. She suggests using speakerphone in private settings only, and generally being mindful of the people around you when taking a call.

“Whether you’re on the street, in a coffee shop, or even on public transport, the goal is to minimize the impact your conversation has on everyone around you. Being discreet and respectful makes all the difference,” she said.

Despite my fascination with this slice of human behavior, there hasn’t been much academic interest. Ayduk said she wasn’t aware of any scientific studies or journals published on the matter. (Free research paper idea for anyone who wants it!)

In the meantime, the conduct will remain a mystery to me. But people are complicated, after all. That’s what makes them so interesting to study.