1
general::
Phrase(s): foul one’s own nest
Fig. to harm one’s own interests; to bring disadvantage upon oneself. (Alludes to a bird excreting into its own nest. See also It’s an ill bird that fouls its own nest.) • He tried to discredit a fellow senator with the president, but just succeeded in fouling his own nest. • The boss really dislikes Mary. She certainly fouled her own nest when she spread those rumors about him.
McGrawhill's American Idioms And Phrasal Verbs