what's that got to do with the price of cheese in China
The phrase is used to mean “How is this relevant to the conversation?”, especially if a person seems to be actively avoiding the topic being discussed.
Me: Hey, do you have that $20 bucks you owe me.
Him: Hey, have you seen the movie Hot Tub Time Machine yet?.
Me: What's that got to do with the price of cheese in China?
Him: Hey, have you seen the movie Hot Tub Time Machine yet?.
Me: What's that got to do with the price of cheese in China?