When combined, the characters literally mean “people and gods are furious together.” This paints a vivid picture of a crime so terrible that all beings, mortal and divine, are united in their outrage.
The power of `人神共愤` is deeply rooted in traditional Chinese thought, particularly the concept of Tian (天), often translated as Heaven. In this worldview, Heaven is not just the sky, but a conscious, cosmic force that oversees the moral order of the universe. The Emperor's right to rule, for instance, was based on the “Mandate of Heaven” (天命, Tiānmìng), which could be lost if he ruled unjustly. An act that is `人神共愤` is one that so gravely violates this cosmic and moral order that it offends Heaven itself. It's an act against nature and justice.
This is a very strong and formal term. Using it for a minor issue would sound overly dramatic and even absurd.