Rhyming Slang.

No-one is quite sure how rhyming slang first got started in the East End. Some say it was used by the criminal underclasses to confuse the police, others think it was joke that got out of hand. Whatever, it's still going strong, still evolving, and still proving to be as confusing to insiders as it is to those its supposed to confuse.

For the uninitiated, this is how rhyming slang works:

First choose the word you want to encode in to slang, eg 'stairs'.
Find a rhyme. make sure it has two parts. eg. 'apples and pears'.
Now only use the bit that doesn't rhyme. eg 'I'm going up the apples'.

A few examples:

Trouble - Trouble and strife - wife
Currant - currant bun - sun
Butchers - butcher's hook - look
Loaf - loaf of bread - head
Chalfonts - Chalfont St Giles (town in the Chilterns) - piles
Tonys - Tony Blair - Flares (the trousers)
Lionels - Lionel Blair (dancer) - Flares (archaic usage)
Britneys - Britney Spears - beers

My personal favourite comes from academia. When you graduate you get awarded a grade - a first, an upper second (or a 2.1) or a lower second (a 2.2), also known as a Desmond.

I though I'd made up all my rhymes for cat, but two of them already appear in the online Cockney Rhyming Slang Dictionary.