What's that got to do with the price of eggs?

This expression is often used instead of saying, 'What's that got to do with what we are talking about?' In other words, telling someone that what they are saying is irrelevant to the matter under discussion. The expression is first attested in America from the late 19th century, but virtually anything can be and has been substituted for 'eggs'. 'Tea in China', 'beans', 'coffee', 'cocoa', 'lemons', 'fish' have all been used, and probably countless others, but 'eggs' is probably still the favourite, for now.