so what - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Who cares? What does it matter? For example, You're not going to the beach today? Well, so what, you can go tomorrow, or So what if she left without saying goodbye—she'll call you, I'm sure. [First half of 1900s] Also see what of it.