Cockney rhyming slang absolutely baffles me.
You take a pair of words in common usage, one of which rhymes with the word you mean, but you use the non-rhyming word in its place. So, there's a soccer team in the west country called Bristol City. "City" rhymes with "Tittie", so instead of saying "Look at them titties!", you say "Check out them Bristols".
Sometimes the word association goes a few layers deep, which is why it can be impenetrable to the uninitiated. For example: Jacobs = testicles. Here it is in a sentence:
Stop me again when I'm walking, and I'll cut your fucking Jacobs off!
Here's how that comes about: Jacobs is a company that manufactures a delicious product called "Cream Crackers"*. "Crackers" rhymes with "knackers", which is simple slang (not rhyming slang) for testicles. It makes little sense but sort of follows the rules. The whole point behind rhyming slang is for it to be gibberish to those outside the "know" - it was invented on the London docks so that the dockers could slag off their bosses without them knowing it.
* Take the Cream Cracker Challenge! Eat two in two minutes without drinking anything.
More rhyming slang (remember, only the non-rhyming word is used):
Butcher's Hook = look..."Let's 'ave a butcher's!"
Lady Godiva = fiver..."Here's the lady I owe ya!"
Apples and Pears = stairs..."It's Friday night, love. Get up them apples!"
China plate = mate..."How ya doin' me old china!"
Barnet Fair = hair..."Fuck me! What 'ave you done to your barnet?"
Pork pies - lies..."You telling me porkies?"
Trouble and strife = wife..."Quiet lads! I've got me trouble on the phone."
Tomfoolery = jewelery..."I bought me bird some tom for her birthday."
Boat race - face..."'Allo darlin'. You wanna come on my boat?"
Rasberry tart = fart..."Who blew a rasberry?" (And you wondered where
that came from)
Plates of meat = feet..."Get yer plates off my nice furniture!"
Skyrocket = pocket..."How much dosh you got in your sky?"
and many, many more.