A recently discovered achievement in which a person headbangs to the degree of which their cranium is placed in their rectum. A person who achieves Cranium-Rectum Inversion is considered one of the Metal Gods.
Metalhead 1: Watch me achieve Cranium-Rectum Inversion.
Metalhead 2: No way.
*Metalhead 1 achieves Cranium-Rectum Inversion and becomes a God*
Metalhead 2: Awesome!