But, this is why Bristol = titty. It’s called Cockney Rhyming Slang.
Bristol = Bristol City = titty. Titty rhymes with city.
Cockney rhyming slang is a form of English slang which originated in the East End of London. It developed as a way of obscuring the meaning of sentences to those who did not understand the slang, though it remains a matter of speculation whether this was a linguistic accident, or whether it was developed intentionally to assist criminals or to maintain a particular community.