foul one's (own) nest
To do something that creates problems for oneself. I wouldn't talk to the boss while you're angry—you'll just end up fouling your own nest.
foul one's nest
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]