Treat somebody like dirt
Definition 1 of 1
Pro Tip 1/3Negative Connotations
This phrase strongly expresses disrespect and should be used with caution due to its harshness. 
John's remarks about her work were so cruel, he was treating her like dirt.
Pro Tip 2/3Emotional Impact
Using this phrase showcases the speaker's disapproval of how someone is being treated. 
When he ignored her contribution to the project, he was treating her like dirt.
Pro Tip 3/3Informal Expression
It's informal and best used in casual conversations, not in formal contexts like business or writing. 
I quit the job because my boss treated me like dirt.