treat like dirt
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.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.