One tear? Good. Waterworks? Bad.

NEW YORK -- “Please, please, please, just give the dog back,” Ellen DeGeneres said weeping on national TV last week. It was a moment that quickly established itself in the pop culture firmament, less for the plight of Iggy the adopted terrier than for the copious crying itself.

Setting aside the question of whether those sobs were 100% genuine, tears are a natural human response, and public figures are obviously not immune. But some who study this most basic expression of feeling will tell you that in this day and age, it can be easier for a crying man to be taken seriously than a crying woman.

In politics, it’s a far cry (OK, pun intended) from 1972, when Sen. Edmund Muskie’s presidential campaign was derailed by what were perceived to be tears in response to a newspaper attack on his wife. Whether he actually cried is still up for debate. But decades later, an occasional Clintonesque tear is seen as a positive thing.

Bill Clinton, that is.

“Bill could cry, and did, but Hillary can’t,” says Tom Lutz, a professor at UC Riverside who wrote an exhaustive history of crying. In other words, the same tearful response that would be seen as sensitivity in Bill could be seen as a lack of control in his wife.

But there are additional rules for acceptable public crying. “We’re talking about dropping a tear,” Lutz notes, “no more than a tear or two.” And it all depends on the perceived seriousness of the subject matter. Thus Jon Stewart or David Letterman could choke up with impunity just after 9/11. But a dog-adoption problem is a whole other matter.

In a recently published study at Penn State, researchers sought to explore differing perceptions of crying in men and women, presenting their 284 subjects with a series of hypothetical vignettes.

What they found is that reactions depended on the type of crying, and who was doing it. A moist eye was viewed much more positively than open crying, and males got the most positive responses.

“Women are not making it up when they say they’re damned if they do, damned if they don’t,” said Stephanie Shields, the psychology professor who conducted the study. “If you don’t express any emotion, you’re seen as not human, like Mr. Spock on ‘Star Trek,’ ” she said. “But too much crying, or the wrong kind, and you’re labeled as overemotional, out of control and possibly irrational.”

That comes as no surprise to Suzyn Waldman, a well-known broadcaster of Yankee games on New York’s WCBS Radio.

Earlier this month, she choked up for several seconds on live radio after the Yankees had just been eliminated from the playoffs. She was describing the scene as manager Joe Torre’s coaches choked up themselves, watching him at the podium and foreseeing the end of an era.

Her tearful report quickly became an Internet hit, and she was mocked far and wide, especially on radio, with her voice, for example, played over the song “Big Girls Don’t Cry.”

“This turned into something pretty ugly,” Waldman said in an interview. “I don’t throw around the word ‘sexist,’ but this was as sexist as it gets.”

There seem to be few limits on crying if you’re an entertainment figure. Johnny Carson’s tears were touching at the end of his career, while serenaded by Bette Midler. As for award shows, aren’t we even a little disappointed (and bored) when a winner doesn’t cry?

But in DeGeneres’ case, along with the strong support from fans and many dog lovers, she also endured some criticism and mockery, especially from fellow comic Bill Maher.

Maher decided to respond on behalf of an entire gender: The opposite one.

“At this moment when the entire nation is saying, ‘Hmm, can we have a woman president? Maybe they’re too emotional,’ I don’t think this is helping,” Maher said on his talk show.