Well, here are some cultural terms, not necessarily euphemisms, but maybe:

From England - John Thomas (penis) Lady Jane (vagina) D.H. Lawrence, just to be outrageous, titled a novel of his "John Thomas and Lady Jane". It was the first draft of "Lady Chatterley's Lover" and is said to be actually a better book than the more famous one. I read both back in my early 20's, and I think JT & LJ is the better of the two.

From China - Jade Stem (penis), Turtle Head (penis), and numerous other poetic terms. These are from the taoist tradition. They saw sex not as a moral matter, but a health matter, and they were quite correct, in fact. Jade Gate was the vagina, which had, again, many other poetically descriptive names.

Common American slang - whanger, tool

Not hard to see how American civilization rates when you compare it to Taoism... :-)