Cut somebody dead
Definition 1 of 1
Pro Tip 1/3Social Rudeness
Used when someone is deliberately ignoring a person in social settings to express contempt or disapproval. 
At the reunion, when John approached, Mary turned away and cut him dead.
Pro Tip 2/3Harsh Consequences
It's a strong phrase indicating that the ignored person might be shocked or hurt by such treatment. 
After the rumor spread, her friends cut her dead in the hallway.
Pro Tip 3/3Social Cues
Pay attention to body language and tone of voice which often accompany this phrase to show disapproval or anger. 
Despite his apologies, she just gave him a cold look and cut him dead.