How many times have you been in flagrante with some dude, having a perfectly nice time, when he begins a series of inquiries as to whether you've come. Then after he's done, he looks up (or down!) at you with a look of confusion and asks, "Why didn't you finish?" Sure, many men don't know that as few as 7% of women can reliably come from vaginal penetration alone — in which case, do you really want to sleep with them? — but for those who do, now they can just look at our vaginas for clues! New research might explain why some women are able to come from vaginal intercourse alone, and most women aren't. According to the Los Angeles Times, it's something called "the rule of thumb": "Clitoris-vagina distances less than 2.5 cm — that's roughly from the tip of your thumb to your first knuckle — tend to yield reliable orgasms during sex."
Basically, if your clit is close to your vagina (C-V distance), you can come from sex. If not, you're S.O.L. Kim Wallen, a professor of psychology and behavioral neuroendocrinology at Emory University, is the one studying the C-V distance theory, but he isn't the first to notice a correlation. According to the L.A. Times:
In the 1920s, Princess Marie Bonaparte, a French psychoanalyst and close friend of Sigmund Freud, grew fed up with her own lack of orgasmic response. In her professional practice, she saw plenty of patients with the same complaint ("frigidity," in the parlance of the day). She blamed physiology, not psyche. Bonaparte collected C-V and orgasm data from her patients and in 1924 delicately published her observations under a pseudonym. (She also persuaded an Austrian surgeon to experiment on her, by cutting around her clitoris and stretching it closer to her vagina — with disappointing results.)
Yikes! If your C-V distance is the size of an end zone, don't fret. Wallen thinks the difficulty of achieving easy female orgasm during intercourse can inspire couples to be more inventive in the sack, though he is concerned that women might feel that a small C-V distance is just another standard women might feel inadequate about, like breast size. "People would ask, 'Is your distance really small?'" Wallen suspects. "Suspects"? Cosmopolitan will certainly find a way!
Female Orgasms And A 'Rule Of Thumb' [Los Angeles Times]