Eat dirt
Definition 1 of 3
Pro Tip 1/3Humiliation Emphasis
The phrase is often used to highlight a strong sense of humiliation or embarrassment. 
After losing the debate, he had to eat dirt.
Pro Tip 2/3Power Dynamics
Usually implies a power imbalance where the person eating dirt is in a lower position. 
The boss's criticism made her eat dirt.
Pro Tip 3/3Confrontational Contexts
Often used in contexts where there's a confrontation or a mistake has been made. 
He talked big but ended up eating dirt.