A pungent, strong, rotten smell expelled from ones mouth 4 feet in diameter. It's similar to warm protein farts in the back of a garbage truck on a hot summer day. it will make you shed a tear. If you are ever near anyone with Nancy Breath turn around and get as far away as possible FAST. The bottom of a joggers sneaker smells better.
John: hey mark did you smell the Nancy Breath on that waitress?
Mark: weew John, that breath is fucking gross. It's like warm protein farts in the back of a garbage truck!