Yesterday, I posted about the word swazzle. I was led to that from the Wikipedia article about Polari:
“Polari […] is a form of cant slang used in Britain by some actors, circus and fairground showmen, professional wrestlers, merchant navy sailors, criminals, prostitutes, and the gay subculture. There is some debate about its origins, but it can be traced back to at least the 19th century and possibly the 16th century. There is a long-standing connection with Punch and Judy street puppet performers who traditionally used Polari to converse.”
That page also includes a brief Polari glossary, and more info about its origins and use:
Polari is a mixture of Romance (Italian or Mediterranean Lingua Franca), Romani, London slang, backslang, rhyming slang, sailor slang, and thieves' cant. Later it expanded to contain words from the Yiddish language and from 1960s drug subculture slang. It was a constantly developing form of language, with a small core lexicon of about 20 words … and over 500 other lesser known words.
Polari was used in London fishmarkets, the theatre, fairgrounds and circuses, hence the many borrowings from Romani. As many homosexual men worked in theatrical entertainment it was also used among the gay subculture, at a time when homosexual activity was illegal, to disguise homosexuals from hostile outsiders and undercover policemen. It was also used extensively in the British Merchant Navy, where many gay men joined ocean liners and cruise ships as waiters, stewards and entertainers.
The almost identical Parlyaree has been spoken in fairgrounds since at least the seventeenth century and continues to be used by show travellers in England and Scotland.