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It's easy to find reliable stats on penis size, but is there anything out there on average vaginal width and depth? I know: The vagina isn't a constant size, it expands with arousal, etc., but the same could be said of penises, and lab-coated experts have managed to measure them. I've tried to measure with a dildo, and been surprised to notice that even at my most aroused, I can only get it about five inches in. Is this unusually shallow?
Also, does it make a difference to most men? If a guy's got a long dick and the woman is (anatomically) shallow, does that substantially decrease the fun? Or is it analogous to the vagina having almost all its nerves in the first third, so that many women don't care all that much about length? Can you ask around, even if there are no concrete facts?
Running your letter here counts as "asking around," doesn't it? Is anyone interested in marking off a seven- or eight-inch dildo (is there anything a Sharpie cannot do?) and sending me the results? (Do not send me the dildo itself, thanks.) Numbers will be crunched. Maybe I'll make a chart.
It's much harder to measure vaginal depth than penile length, and that (along with the fact that fewer women than men actually give a crap about this issue) is the probable explanation for the dearth of info. Not only does the vagina constantly shape-shift, as you noted, but there doesn't seem to be much of a consensus on what we'd be measuring if we did bother to measure. Many of the sites I checked out, for instance, cite distance to cervix as the measurement of interest, and anyone who's spent much time up anybody's hoo-ha ought to know that there's a little fractal fillip of space like the tail on whatever you'd call a single paisley (a paisle?) extending under and behind the cervix, even when the hoo-ha in question is at rest. At play, when the vagina widens and loosens, and especially as the uterus begins to lift up and out of the way, taking the cervix with it, this space may become capacious enough to stash any number of interesting objects. A fist, say, or one of those bananas an emergency room doctor told me he was always fishing out of college girls who'd hygienically, if ill-advisedly, peeled their fruit before deploying it. So what are we measuring? And how are we determining where, exactly, the vagina begins, let alone ends? Are we including the vulva, some of which are bony while others are plush? And what about position? Have you tried measuring while kneeling, as well as while supine or prone? Rear-entry as well as from the front?
Men generally do enjoy the feeling of being completely engulfed during intercourse, and inconveniently for us but happily for them, the base of the penis is not substantially less sensitive than the front half (although most men do have more feeling in the head, or glans). Most couples, however, can pretty easily achieve that "all the way in" feeling by adjusting positions, propping things on pillows, and so on. If that doesn't work, a hand, yours or his, can be put to good use here, but you know, I don't think there's a thing wrong with you, and why solve a problem you don't even have?
I think your response to "I Wanna Be Great," the girl whose boyfriend kept (unfavorably) comparing her with his ex, was on point. What I find strange is that women always want to know "how good" they are in comparison to past partners. I always respond that I cannot compare sex partners because each partner means different things to me. I have no desire to know how I compare with past partners. Is there some gene in women that makes them want to know this? I do usually tell them that they are the best and that is why I'm with them (hey, a little white lie for the sake of the relationship can't be that bad). Why do women want this information?
I assume your only experience has been with women, so I suppose it's natural to go looking for the "rate me!" trait on the X chromosome, but let me tell you, you won't find it there. In my fairly vast experience (answering questions! I'm not talking about the other kind here), it is, if anyone, men who fret the most about performance and worry that a partner's former partners will somehow outshine them. But I can't prove it's mostly guys who annoy in this very particular fashion, and it doesn't really even matter. The truth is, everybody does it; you just haven't done it with everybody.
And by the way, your little white lie sounds a bit cheesy — and don't think the girls haven't noticed. Flatter, but don't blow smoke. It isn't nice.