something else again
something else again {n. phr.}
A different kind of thing; something different.
I don't care if you borrow my dictionary sometimes, but taking it without asking and keeping it is something else again.
"But I don't want a new car," Charles said to the car dealer, "I want a used car." "Oh," said the car dealer, "that's something else again."
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Source: A Dictionary of American Idioms