During the December festival of Saturnalia, Romans threw their social norms out the window. Not only did everyone party, eat, drink and gamble but they also switched roles. The masters served banquets to their slaves and slaves were allowed to disrespect their masters.
According to Wikipedia, Roman citizens (a privileged political and legal status) normally went about bare-headed, but for Saturnalia they wore the pileus, the conical felt cap that was the mark of a former slave (freedman). Slaves were not ordinarily entitled to wear the pileus but they wore it during Saturnalia, too. Everyone was pileated.
Just like this woodpecker.
(photo by Dick Martin)