^ From what's known as the "East End" in London, but it's pretty close to the middle and is North of the river Thames. My Stepdad's from a different part of London, but knew a fair bit of rhyming slang, and he had the right accent too (some of them don't rhyme unless you have a Londoner's vowels!)
There are a few common ones that a lot of Brits would know, but possibly wouldn't know they were all from rhyming slang...
"Have a butchers" = "Have a look" (butcher's hook -> look)
"Blow a raspberry" = making a farty noise with your lips (raspberry tart -> fart)
"Use your loaf!" = "Use your head!", Think! (loaf of bread -> head)
"Berk" = an insult (Berkeley Hunt -> erm...I'll let you guess, it's a bit rude!)
It only got started in Victorian times, IIRC, and it may have been so cryptic on purpose, to allow open speaking that outsiders and/or the police couldn't understand (i.e. a cryptolect or a thieves' cant). The East End was traditionally one of the poorest areas of London, and had a reputation for being a very close-knit community with a thriving black-market.
_________________
When you are fighting an invisible monster, first throw a bucket of paint over it.