CRACKED Magazine offers a scatalogical look at Japan's Insane Creation Myths. "Hoo boy", I thought, "here comes another bunch of wild exaggerations to play up the 'Japan is so crazy' meme".
Well... I'll leave specific criticisms to experts in the field, but a scan of the linked references suggests that, yeah, these myths are built from the distilled essence of porn movies and junior-high body function jokes. Which isn't unique to the ancient myths of Japan, as many commenters point out, but these particular myths sure do aim for the gutter.
Fun stuff, if you're not too easily offended!