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Why do guys take crotch shots, anyway?

Susan Walsh / AP

Rep. Anthony Weiner, D-N.Y., waits for an elevator near his office on Capitol Hill in Washington on Thursday.

The flashes -- both the news and nether region variety -- seem to be popping up everywhere lately: Brett Favre allegedly aired it out and Kanye West snapped south of the border.

After a lewd photo was sent from Rep. Anthony Weiner's Twitter account, the aptly dubbed “Weinergate” saga has exposed a truly touchy question for the Tech Age: Why are some dudes compelled to take cell phone pics of their private parts then share those images -- via texts or tweets -- with the ladies?

It’s time to apply some psychological expertise -- let’s call it “junk” science -- to this sexting obsession among some fellas.

“The simplest theory for the behavior,” said Marta Meana, president of the Society for Sex Therapy and Research, “is that these men think the photos will serve to arouse the woman – because they, themselves, would find it arousing if that woman sent such a photo to them.”

Here’s the rub: that theory applies only to men who send down-and-dirty close-ups to women they know. If a sexter sends an unsolicited, digital portrait of his genitals to a woman he doesn’t know, “it is likely that the act … is arousing to the sender -- sub-clinical or clinical exhibitionism,” said Meana, also a psychology professor at the University of Nevada, Las Vegas. “The primary intent … is to arouse themselves.”

That scenario seems fit the three celebrities mentioned above -- if they, in fact, did it. (Update: OK, now we know that Weiner did, in fact, do it.)

Favre, the retired quarterback, was fined $50,000 by the NFL late last year for “failing to cooperate” with a league probe into whether he sent x-rated snaps to former NY Jets employee Jenn Sterger. He has not owned up to what may have been the final sack shot of his career. Sterger said she never met Favre.

West, before fame, gifted some of his female MySpace friends with an unsolicited crotch shot which hit the Internet last year. West subsequently admitted to a radio station that the appendage image was his groin.

And on May 27, a post from New York Congressman Anthony Weiner’s Twitter account linked to an image of a man wearing two things -- gray boxer shorts and an erect penis. That picture was sent to one of Weiner’s Twitter followers -- a 21-year-old college student in Seattle, who Weiner said he didn’t know. The U.S. House member denied posting the photo, but noted he couldn’t say “with certitude” the pic was not of his own privates. Weiner’s spokesman initially said the Congressman’s Twitter account had been hacked.

From ballers to rappers to -- maybe -- lawmakers, Little Willy, Willy won’t stay home.

If nothing else, the latest battle of the bulge put Weiner’s long-time pal Jon Stewart in an awkward place. The tweeted image plus Weiner’s job plus – of course – his ironic name – proved too much for “The Daily Show” not to urge “You’ve got to come cleaner, Weiner” in this hilarious Jon Stewart clip.

Here’s the hard truth, guys: Most women are not turned on by video or digital glimpses of your junk, Meana said.

Empirical literature shows clear differences in what lights the passions of males and females. While many dudes are visual animals focused on sexual anatomy, “women’s subjective arousal appears to be more driven by relationship dynamics, expressions of desire, narrative expositions of that desire,” Meana said.

But some ladies -- especially those already in a physical relationship with the sender -- are into sexting. Still, it’s an erotic fine line.

“Sending such a photo after a sexless first date is probably a misstep -- it skips too many courtship stages,” Meana added.  “Sending such a photo after you have had hot sex could be sexy to some women.”

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Bill Briggs is a frequent contributor to msnbc.com and author of “The Third Miracle.”