I've rabbited on about Cockney Rhyming Slang (CRS) before. Here's a nice video posting explaining CRS. I like Scooby for clue (or should that be clew?).

[H/T to the new Reddit https://www.reddit.com/r/sillylinguistics Silly Lingusitics feed.]

Great explanation. And the link to Reddit had some other wonderful links. I loved the Juke Box.

Most of that was pretty accurate. There were a couple I hadn't heard but that could just be me. I don't think that you can really call things like "It's all gone Pete Tong" cockney rhyming slang though. For me it fails on two counts. First, it isn't cockney. It's used mainly by affluent middle class students affecting the cockney speech patterns and second it's never used in an abbreviated form - no one would just say "It's all gone Pete". Mockney rhyming slang perhaps.

When do you use cockney? Just for fun, or do some people use it regularly?

The rhyming slang, you mean, or Cockney itself? Cockney is a dialect of English spoken by people living in part of London. The rhyming slang originated as a thieves' cant and was deliberately obscure so The Man didn't understand what was being discussed.

It's generally used nowadays for fun, but a lot of people will use elements without realising it. For instance, someone might refer to their hair as their 'Barnet', without realising it comes from rhyming slang - Barnet fair - hair. Nowadays I don't think anyone tries to use it as a thieves' cant

An answer I thought I posted to this seems to have gone missing. You use cockney rhyming slang when you are NOT, yourself, a Cockney but are trying to write a gritty crime drama set in London.