no skin off one's nose

Etymology
This saying has been attributed to originating in boxing as a minor blow taking no skin off. See: The American Heritage Dictionary Of Idioms, Second Edition Paperback – February 26, 2013 by Christine Ammer and Random House Dictionary of America's Popular Proverbs and Sayings: Second Edition Paperback – April 18, 2000 by Gregory Titelman.

Noun

 * 1)  No harm to one.
 * You can be as critical of them as you like. It's no skin off my nose.