treat like dirt - 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.
Behave badly or show contempt toward, as in Her boss treats all the secretaries like dirt. This idiom uses dirt in the sense of “something worthless,” a usage dating from the mid-1300s.