I've personally debunked this myth!
Most women believe height, hand size, finger length, and/or shoe size will all indicate penis size. I have heard grown women cooing over a celebrity after learning that he wears a size 14 shoe. I know from repeated personal experience that this myth is totally untrue.
Two examples, the largest and smallest penises on men I've dated.
Smalled Penis: I have dated 3 men 6'4" or taller. One of these three men had both the thinnest and shortest penis I've ever had sex with. I don't remember his shoe size, but I remember that it was on the large side. This poor guy's penis was so small that I could often barely feel it during sex. He was very self-conscious of his small penis and compensated very well with his enthusiastic oral technique. I had lots and lots of sex with him, despite his small penis because of how much time he spent with his face between my legs. We actually dated for a while.
Largest Penis: The man I am currently with has both the longest and thickest penis I've ever had sex with. It's actually too big and a bit of a problem, but I deal with it because he's worth it. He has the smallest hands I have ever seen on a grown man. The length of his fingers are as short as mine, and I am so petite that I have to wear children's gloves! His palm is much larger than mine, at least 50%, but his hands are much smaller than most men's hands. He is 5'10" and he wears a size 10.5 shoe, both average sizes for men, I believe. He's also got a boyish, young face, and doesn't have a deep voice, so the secondary sex characteristics brought on by testosterone during puberty (square jaw, chiseled features, deep voice, etc) have nothing to do with it either.
There are many more examples I could use, but I think those two probably illustrate my point the best!
You can't tell how large a man's penis is without taking it out of his pants and looking at it erect.
(I would debunk this myth to other women, except that I always feel like I'd be admitting to being a slut and I'd also seem like I was bragging about how large my boyfriend's penis is, which is TMI IRL, so I keep my mouth shut.)