foul one's own nest

/F AW1 L W AH0 N EH0 S OW0 N EH0 S T/
verb
  1. 1

    To damage one's environment.

  2. 2

    To hurt one's own interests, especially to damage the reputation of one's self, family or group.

Source: https://en.wiktionary.org/wiki/foul%20one's%20own%20nest