I noticed a lot of fairly common Asian names — Poon, Dong, Wang — are also slang for genitalia in American English.
Why is this?
(See also: people’s names as names for genitalia, for English names like Peter, Johnson, Dick.)
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.
Long before the names Poon or Dong were common in America (though Wang, or Wong --most Americans don't distinguish them -- has been known here as a Chinese name for over a century), the euphemisms
(for female genitalia), and
(for male genitalia), and many more as well, for both, were making the rounds of the English-speaking world.
English, since its speakers have many strange beliefs and taboos about the power of word magic, has to use an enormous number of euphemisms in order to avoid taboo words. One is reminded of the Nacirema.
These euphemisms change constantly, of course, like any other fashion, and, if allowed to fester, will use up every available syllable.