feather your own nest

Meaning: if you feather your own nest, you use your position or your job illegally for personal gain.

For example:

Almost every corrupted government truly believes it’s accepted in many developing countries that a government official will use their position to feather their own nest, and this is why government salaries are kept so low.
In some countries a Sheriff who feathers their own nest isn’t seen as being corrupt or mafia member; they’re seen as being smart.