Usually when someone does not think your current statement has to do with the conversation at hand they can ask, "What does that have to do with the price of tea in China"?
Where did that form of statement come from?
Eric Partridge, "A Dictionary of Catch Phrases," says this one is a variant of "What's that got to do with the price of eggs?" and has been around "since the 1940s--perhaps influenced by the expression, e.g. 'I wouldn't do that, not for all the tea in China.'" He identifies the "eggs" saying as "US: since the 1920s, if not earlier."
The complete expression is actually the following question: "What does that have to do with the price of tea in China?"
The price of tea in China is completely irrelevant to the subject of conversation. So, when someone asks this question, it means they’re really surprised by the listener's comments. Effectively, they're saying:
The Wikipedia article Irene mentioned is pretty good.
I am going to agree with the "evolution" of a sarcastic answer from a sarcastic answer from a real answer to a real problem: Meaning, originally A LOT of England's money and finance WAS tied up in the price of tea - at the unloading docks in London each year. "Tea races" were highly looked at events covering months of travel and high drama from China around Cape Horn to England to get the first cargo back to London! It affected what everybody drunk and how much everybody bought and paid for their meals and drinks. Very, very important - just like today, the price of oil IS a daily report on the news and in the stock markets.
But, in China, at the China docks? A little bit less important, but relevent. People, companies, industries made their yearly profits - and thus the yearly wages and salaries and earnings for everybody from the owner to the stockholders to the lowest laborer - on how much the difference in price of tea was between the China docks and the London sales rooms. A late ship, a lost ship or spoiled tea product? Disaster. A bad market in China or a bad growing year or famine or a crop failure over there?
No one here seems to have actually answered the question in terms of the origin. The phrase is believed to have begun in 19th century England where the actual price of tea in China was of interest. When someone in the British House of Commons said something others felt was irrelevant, it was met with this saying... meaning, the price of tea in China is a relevant topic, but yours is not.
I was recently wondering the same thing. Reading a book on China's wars with the Mongols 'defending heaven' by James Waterson, it mentions page 118, about the amalgamation of the bureau for Tea and Horses. The Song dynasty was trying to gain extra coffers to buy steppe horses. These were needed in fighting the Mongols. Tea was a great source of revenue for the government. There was always a delicate balance for the Song in managing tea (too little sold = less revenue), (too much sold = price of tea goes down). The price of tea was quite significant. I am not sure if this is its origin but thought I would share. The book is quite a fascinating read also.
I've never heard this precise formation: to me, it sounds like a conflation of two phrases- "What's that got to do with the price of fish?" (alternative: eggs) - which as pointed out above is really expressing surprise, and "I wouldn't do that for all the tea in China" - which is expressing extreme reluctance/aversion (and probably dates from the time when tea was an expensive enough commodity that tea-caddies came with lock, to stop the servants from pilfering it).