其实东亚男人不要怕。 阴道伸缩性很强的（>10cm)就可以。

Penis size and female genital response
According to some sex researchers and therapists, several misconceptions have developed surrounding penile-vaginal intercourse.[44] Many men exaggerate the importance of deep vaginal penetration in stimulating a woman to orgasm.[who?]

The most sensitive area of the female genitals includes the vulva, clitoris, and the section of vagina closest to the outside of a woman\'s body, which is roughly 10 centimeters (4 in) in length. Research has found that portions of the clitoris extend into the vulva and vagina.[45] Given that the median penis size is above this length, the majority of penises are likely of sufficient length to fully satisfy their partners.

While many women find penile stimulation of the cervix to be uncomfortable or painful, others report it to be key to orgasm.[citation needed] The cervix may be confused with the anterior or posterior fornix, the deepest point of the vagina, above and below the cervix, respectively.[46] The cervix and fornix are close to each other, making it possible for there to be indirect and/or simultaneous stimulation between them.[47]

The fornix is said to be another possible orgasm trigger area.[48] Tests have shown that pressure on this area causes the vagina to lubricate very quickly.[49] The area of sexual response in the anterior fornix has also been called the epicentre, T-Spot, AFE-Zone, AFE or A-Spot; while in the posterior fornix it has been called epicenter (as well) or cul-de-sac (since the cul-de-sac, also known as the rectouterine pouch, may be indirectly stimulated by pressure on the posterior fornix[47]).

During arousal, the vagina lengthens rapidly to an average of about 10 centimeters (4 in), but can continue to lengthen in response to pressure.[50] As the woman becomes fully aroused, the vagina tents (last 28260;3 expands in length and width) while the cervix retracts.[51] The walls of the vagina are composed of soft elastic folds of mucous membrane skin which stretch or contract (with support from pelvic muscles) to the size of the penis.[52] This means (with proper arousal) the vagina stretches or contracts to accommodate virtually any size penis, from small to large.[53]
http://en.wikipedia.org/wiki/Human_penis_size