Commentary by Dianne Klein: The notion of privacy, or how much is too much when it comes to exposure, might make the top 10 list for differences among cultures, and not just different national cultures.

A few days ago, a woman whose name I didn't catch spoke to me about turnips, and how her formerly chubby son fashioned a turnip diet that helped him drop 80 pounds but morphed him into an anti-fat zealot who harangues his mum about enjoying a nice slice of cake.

This happens to me often. Complete strangers divulge unsolicited personal information about themselves and their loved ones.

I quite like it. The exchanges provide a small-town vibe in the big city. They're reminders that we're all in this together, this, uh, human condition.

I made a face, though, when I heard about the turnips, which prompted the woman, Irish with a thick brogue, to explain that turnip love is a cultural thing — hers, not mine. A good turnip binge, she suggested, was right up there with "Danny Boy" as a quintessential Irish experience.

I won't forget this woman — not her story nor her other distinguishing characteristics.

Maybe because she was nude.

We were in a gym locker room, and she was slathering moisturizer over hummocks of flesh that she slapped around and disparaged. My own hummocks were not exposed, nor would they be. I tried to keep my gaze above the woman's neck. Too much information.

The notion of privacy, or how much is too much when it comes to exposure, might make the top 10 list for differences among cultures, and not just different national cultures. There are generational differences about privacy, gender differences, differences between reality TV show contestants and most of the rest of us.

And then there's Facebook. Everybody's on Facebook. Or if they're not, they're constantly being told they should be. Facebook as cultural touchstone is a dividing line, a phenomenon now so mainstream that if you're not on Facebook you're thought to be either technologically impaired or so antisocial that you might as well move to a shack off the grid in Idaho and spend your days scrawling angry screeds to newspapers that people actually hold in their hands.

Most of Facebook's more than 400 million users create a profile by answering a few online questions, posting a photo (or many) and soliciting or responding to friend requests. Parents sign up to mortify their children. College students, surely tired of spending money to mail home glossies of frat parties they figure Mom and Dad might enjoy, instead just post everything online. Until they start looking for a job.

And unlike the all-volunteer army of tweeters on Twitter, who indiscriminately market their mood swings, political causes and sexual tastes, there is — or was — a feeling on Facebook that posted information was somehow "restricted" to, you know, 2,436 of your closest friends. And maybe their friends too, and their friends' friends, plus Kevin Bacon.

Then issues came to light. Personal data were said to be exposed and vulnerable to random strangers who could use it for voyeurism, marketing or other nefarious reasons.

Shocking.

Fingers were pointed. Legislators declared their outrage. An attack ad by California attorney general candidate Kamala Harris accused Chris Kelly, her opponent in the Democratic primary, of "designing the Facebook privacy policy condemned across the country," a charge he denied. And even after a chagrined Facebook instituted, to much fanfare, a simplification and tightening of its privacy settings, including an option to turn off "instant personalization," the German consumer protection minister Ilse Aigner invoked the evil Big Brotherism of the Nazis and the East German Stasi and declared it not good enough.

Aigner threatened to shut down her personal Facebook account, thereby defriending her 4,334 Facebook pals. Germany, she said, had higher privacy standards "than elsewhere in the world and America."

Aigner and others across the globe, including a reported 27,000 people who deactivated their accounts on the recent Quit Facebook Day, insist that the site has it backward — that consumers should "opt in" to share information rather than change default settings to "opt out."

"(The) onus is on the individual to manage these choices," the website quitfacebookday.com complained.

But isn't managing one's choices simply taking responsibility for one's decisions? Accepting that responsibility might prompt other questions: Is it wise to post photos of that drunken hookup from last weekend's convention in Las Vegas? How about letting everybody in on your Farmville sheep fanaticism? Or the fact that you "got on board" with Bud Light?

Facebook is saying it's up to us how much we want to reveal. And I'm OK with that. Facebook is not Big Brother, nor should it be Big Nanny.

Facebook and its competitors have a responsibility, of course, to post simple, clearly visible notices warning that one is about to enter a High Exposure Zone. After that, it's up to you to decide to cover up, avert your gaze or frolic in the altogether. Otherwise you are in danger of missing out on the joys of social networking, writ large or small.

Like the turnip thing. Who knew?

Dianne Klein, a former Los Angeles Times staff writer, is a freelance writer in San Francisco. She wrote this for the Times.