My husband and I were visiting friends, and he started walking around their house flossing his teeth. I told him this is not okay, but I couldn't really tell him why. Could you please explain why it's not appropriate to go around flossing so I can tell him and get him to stop?!

--Embarrassed

What's next, margaritas and oral surgery on the deck?

Locking doors didn't get added to bathrooms as some sort of design quirk (like shutters that don't shut on those aluminum siding "Tudor" houses in suburbia). Most of the behaviors we perform in bathrooms aren't all that audience-friendly -- which is surely why we don't see Netflix specials like "Mr. Jones Takes a Poo." Though that activity, like flossing, has health benefits, the rest of us don't need to bear witness. In fact, we're grossed out if we have to -- and we seem to have evolved to feel that way.

Evolutionary psychologist Joshua M. Tybur, who researches disgust, explains that our capacity for getting grossed out seems to help us avoid disease-causing microorganisms, which could put a crimp in our being able to survive and pass on our genes. Disgust basically acts as a psychological "Keep Out!" sign when we encounter things that could infect us, like bodily fluids, spoiled foods, insects, rodents, and dead bodies.

Whether disgust is likely to be triggered is actually the perfect guideline for whether some behavior is a no-go in public. As I put it in my science-based manners book, "Good Manners for Nice People Who Sometimes Say F*ck," "consider how pathogens are spread from person to person. If whatever behavior you're contemplating could cause some bit of something -- a piece of chewed food or some bodily icky -- to go airborne, it's bathroom behavior." Explain this to your husband. Ideally, if he has some news to share with your friends, it isn't something along the lines of "Oh, my bad -- a speck of cilantro from last week's sandwich just hit your light fixture."