Or crud in their eye?

Or something visibly dangling from their nose?

Or a big gob of hair askew (hopefully not from a "There's Something About Mary" episode).

Face it, there's just no good way to tell a friend, much less a stranger, that a large zit on their face is distracting.

"Every single human being on the planet has had spinach on the teeth, something creeping out of their nose, or toilet paper on their shoes," says Kristin Perrotta, deputy editor and beauty director of Allure magazine. "That's why I think it's your obligation as a human being to point it out. There's a good way, and there's a humiliating way."

Ah, but there's the rub. Most of us don't care to learn the difference because it's easier to walk away from Miss Lipstick on the Teeth and Mr. Open Fly than to deal directly.

Mother and father may have taught us how to eat properly and to open doors for ladies, but they skirted the sticky terrain of how to deal with an associate's bad breath or a friend's copious nose hair. Why? Because nobody taught them either. Social etiquette skipped the chapters on how to deal with someone sporting a blizzard of dandruff on a navy blazer.

For a society that delights in practical jokes, embarrassing home videos and no-secret-is-too-personal tell-alls, we suddenly become incapacitated when it comes to informing a friend or co-worker about these embarrassing personal matters.

"Most people aren't comfortable doing it," says business etiquette expert Lydia Ramsey, author of "Manners That Sell: Adding the Polish That Builds Profits." "But once you've done it several times you realize that people appreciate it."

Do they? Does anyone really want to be told they have drool on their chin?

"I think honesty is usually the best policy. But what you want to avoid is cruel honesty," says Lesley Carlin McElhattan, who along with Honore McDonough Ervin constitute the Etiquette Grrls, authors of "Things You Need to Be Told" and "More Things You Need to Be Told."

McElhattan says common sense should guide you.

"We are hesitant about saying something because we're concerned about insulting the other person by telling them. I think that's a very valid concern," says McElhattan, whose Etiquette Grrls Web site, www.etiquettegrrls.com, traffics in these social dilemmas. "I think it's good that people are hesitant to say something because if you don't know how to handle it, it can come out sounding harsher than it's meant to be or misinterpreted."

The key, she says, is "if it were you, would you want someone to tell you?" In some cases, the answer is no.

"A zit on your nose? You pretty much know you have it, so you don't need anyone to tell you. If it's something embarrassing about the appearance that they can't do something about, then it's not worth the trouble," she says.

The best way to point out these potentially embarrassing situations is to do it privately. If you're in a social situation, move the person away from the crowd so nobody else can hear.

Perrotta says etiquette books don't often cover this ground because the rules aren't fixed.

"A lot of etiquette books unfortunately assume that we all walk around naturally perfect and fabulous, and these gross things don't happen," she says. "It's stuff you learn being a social person."

Which brings us to the unfortunate truth that we aren't the social people we used to be. As we become a busier society and the Internet becomes a more familiar mode of social communication, our ability to learn the rules that govern one-on-one social interaction fades.

"It makes me think that people don't look after each other in the same way they used to. Or pay attention to each other," Ramsey says.

Which she says is a shame.

"Just smiling and being nice and doing things for people that you don't know is good," she says.

Even if it means telling them they have spinach on their teeth?

Yes, Ramsey says. "Maybe it's a start at building some kind of a relationship, which we just don't do enough anymore. We ought to do more of that.