How did a crushing public humiliation become known as a “Roman holiday”?

The Etruscans of ancient Italy ritually honoured their dead war heroes by sacrificing the lives of all prisoners seized in battle. After conquering the Etruscans, the Romans borrowed and embellished the ritual by having the prisoners kill each other. They turned the slaughter into public gladiatorial games and declared the spectacle a Roman holiday, which became an expression synonymous with any cruel and crushing public destruction.