Also, foul one's own nest. Hurt one's own interests, as in With his constant complaints about his wife, he's only fouling his own nest. This metaphoric expression transfers a bird's soiling of its nest to human behavior. [Mid-1200s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.