Thick green- or yellow-colored mucus that is produced as a result of a respiratory disease or infection and coughed up out of the mouth; phlegm. My grandmother always kept a pack of tissues in her pocket that she could spit her lung butter into after she had a coughing fit. Look, I get it—you're sick. But at least have the decency to rinse the lung butter down the drain after you spit it into the sink!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
n. vomit. God, you got lung-butter on my shoe!
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.