Polari is a form of cant slang adopted by the queer subculture in England throughout the nineteenth and most of the twentieth centuries. Its origins are murky, although there’s evidence at least some of it dates back as early as the 1500s, where it was used by a number of socially marginalised groups, including actors, circus showmen, merchant seamen, prostitutes, and petty criminals, as well as queer men. Punch and Judy street performers also have a strong association with it.
The purpose of any slang vernacular is to include and exclude, and usually serves to mark the speakers out from the dominant culture. People use slang all the time — it exist in different occupations (I could write a whole essay on the shorthands, abbreviations, and slang of the construction industry, for a start), different age groups (teenagers are most notable for it), and across different socio-economic strata. Geographically, we use different words depending on where we’re from (dialect), and individually, too (idiolect). Close-knit groups of friends will often develop their own words (or ascribe new meaning to old ones) based on common experience, and using language in this way encourages social cohesion, both by linking all the users with a common tongue, and by excluding those who are “other.”
When we’re talking about a subculture which exists beyond the law, slang also enables free speech in places where being overhead could be dangerous.
Because new words are rarely coined out of thin air (most of Shakespeare’s contribution of 1700+ common words to the English language were back-formations or created using new prefixes or suffixes), Polari has tracable roots in several existing languages, including Romance (Italian or Mediterranean Lingua Franca) and Romani, and Yiddish, as well as borrowing heavily from existing London slang, backslang, rhyming slang, and the vocabulary of sailors and thieves. It almost certainly evolved from Parlyaree, a fairground language dating from at least the seventeenth century, and crossed to the theatrical set though travelling shows.
The existence of another language in the midst of England didn’t go unnoticed. As early as the 1850s, the English social reformer Henry Mayhew published some examples of Polari gleaned from a Punch and Judy showman, but it wasn’t until the 1960s that Polari became accessible to everyday people. Its introduction to the mainstream came in a BBC radio show, Round the Horne, which featured a pair of luvvie thespians — Julian and Sandy — who spoke largely in Polari. Most of the listeners probably didn’t follow every word, but Polari is a quick and witty language which sounds funny even if you’re struggling to decipher the punchline. (And if you’re wondering what it’s like to half-understand a slang language, watch A Clockwork Orange.) Slang benefits from being relatively simple to pick up (too complicated and it would quickly fall out of use), but complex enough that a casual listener wouldn’t be completely sure what was being said.
The success of Round the Horne was a disaster for Polari. Underground slang languages work precisely by remaining in the shadows, and once it was being broadcast regularly by the BBC, it ceased to be useful to its original speakers. At the same time, the early gay rights movement deliberately distanced themselves from it, seeing it as divisive at a time they wanted to integrate, and derided it because most of the words of Polari concerned themselves with sex, bitching, and gossip.
Polari has undergone something of a mini-revival since the mid-1990s, but the interest is largely academic. It doesn’t seem likely it will ever return to what it was, although some of its words live on in the common vernacular: “bold” for daring; “butch” for a masculine lesbian; “camp” for effeminate; “khazi” for toilet; “chicken” for a young gay man; “cottage” for a public toilet where men meet for sex; “dish” or “dishy” for attractive; “dizzy” for scatterbrained; “drag” for women’s clothes; “fruit” for an especially flamboyant gay man; “mince” for an affected walk; “naff” for bad; “scarper” for running away; “slap” for makeup; and “troll” for walking about, especially looking for sex.