Words are fun!

Rhyming slang started with the street traders in the 19C. The traders (costamongers) would go to the market or even go out of London to growers to buy and sell fresh fruit and veg off a donkey cart. They were an urban peasantry who did not fit into the new industrial society. The newly founded police force was given the task of placing them under control. (Weights and measures, controlling pitches, banning traditional fares, banning street games, they even had the right to inspect homes for cleanliness.)Huge street battles were fought until the police got the upper hand. Suddenly the coppers were watching what ever they were doing so the use of Romany, Cant, back slang, and rhyming slang became methods of concealing what you were talking about. Some of the early use has become "legitimate". A "Mickey Finn" comes from the instruction to put a strong laxative into a police agents beer- Mix one in- Mickey Finn. Today in parliament the aristocratic Eton and Oxford educated David Cameron (leader of the Conservative Party) talked about the Prime Minister "loosing his bottle"
Bottle and Glass- ass. A native user like me would seldom use bottle. I would string it through a bit. April- April in Paris. Paris rhymes with Aris -Aristotle. Aristotle- bottle. Bottle and glass- ass.
New ones are made up all the time- "Who is getting the Britneys in?" (Britney Spears- Beers)
Historical ones like Tom Micks- six. Or Lillian Gish- fish are from the silent film era.
My favourite is Jerusalem for donkey. Jerusalem artichoke to rhyme with the Romany word for donkey; moke.
Back slang is still in the language ;Yob (boy backwards).
A gay language also evolved amongst male prostitutes and with theatricals. I did know some lovely old queens who spoke it quite fluently. I can remember some phrases "Dolly to vader your bona eek" Lovely to see you beautiful face. I believe it is fashionable again in high camp circles in London. Bona.
For some real fun catch this!
http://www.youtube.com/watch?v=9ak5vYS0tvg