the scum of the earth
The absolute worst kind of person or people. The phrase comes from the Bible. The people who carried out those atrocities are the scum of the earth.
the ˌscum of the ˈearth
(informal) a person or a group of people thought to be worthless, evil or completely without good qualities: Drug dealers are the scum of the earth. OPPOSITE: the salt of the earth Scum is a layer of dirt on the surface of water.