drive a nail into one's coffin
To do something that causes you serious and permanent harm: “I told my uncle that every time he lights a cigarette, he's driving another nail into his coffin.”
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.