Also, what's it to you? What does it matter? Also, how does it concern or interest you? For example, I know I don't need another coat but what of it?—I like this one, or What's it to you how many hours I sleep at night? The first term, a synonym of so what, dates from the late 1500s; the second, another way of saying “mind your own business,” dates from the early 1900s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.