Apparently this is also considered to be Scottish rhyming slang too (as used in the film Trainspotting), but my old man used to say it so I'm having it as Cockney.
Joe Baksi was an American heavyweight boxer in the 1940s and 1950s.
Joe Baxi is rhyming slang for taxi.
Let's use it in a sentence:
"Oy, Joe Baxi", which translates to "Oy, taxi"