To foul one’s own nest
Ã¢â‚¬Å“To foul oneÃ¢â‚¬â„¢s own nest.Ã¢â‚¬Â
This expression probably comes from the fact that many birds are careful not to foul their own nests. The droppings of the young are picked up from the nest by the adult birds and dropped on to the ground below the nest. There has been a proverb in existence for over a thousand years which says, Ã¢â‚¬Å“It is a foul bird that defiles its own nest.Ã¢â‚¬Â
This idiom means simply to harm oneÃ¢â‚¬â„¢s own interests.
Ã¢â‚¬Å“By not picking up things after their teenage son, they allowed him to foul his own nest.Ã¢â‚¬Â