The word merkin is one of the perpetual bad puns of the Internet. I first came across it in the Usenet newsgroup alt.fan.pratchett (a group devoted to the works of the British fantasy writer Terry Pratchett, he of the Discworld fantasies) and it puzzled me. From context, it seemed to be used as a synonym for inhabitant of the United States of America but it only slowly dawned on me that those who used it were guying a supposed half-swallowed pronunciation of “American” by some Americans, particularly the late Lyndon Johnson.
Then I looked it up and the full force of the pun hit me. The word actually has a number of senses, all of them sexually-related and, therefore, highly risible to persons of a certain cast of mind. One of the current standard ones is pubic wig (such wigs are used, apparently, in the theatrical and film worlds as modesty devices in nude scenes). It can also be a contrivance used by male cross-dressers to imitate the female genitals. Another sense which is even lower slang and which came into the language last century is, as Eric Partridge delicately puts it in A Dictionary of Historical Slang, “an artificial vagina for lonely men”.
The OED says that its first use in English, in the sixteenth century, was as a term for the female genitals, but then its sense transferred to the pubic hair, and from there to artificial pubic hair and then much later to an artificial vagina. Such is the shifting and inconsistent nature of vocabulary, at least when the word concerns intimate matters not often spoken of in public nor written down.
Various people on the alt.usage.english newsgroup (Mark Israel, Paul Andresen, Mark Brader) have recently been discussing Stanley Kubrick’s 1964 film Dr Strangelove, which named the character of the President, one of the parts played by Peter Sellers, as “Merkin Muffley”. This gets two risqué usages past the censor at once, since “muff” is another slang term for the female genitals (as in muff-diving for cunnilingus). This name was presumably the work of Kubrick or his scriptwriters, since the book on which the film was based (Red Alert by Peter Bryant, pseudonym of the late Peter George), does not name the presidential character.
No doubt you will understand now why the use of Merkin in Usenet posts is usually restricted to non-Americans ...