It’s no surprise the rowdy roots of Christmas come from a culture marked by excess- the Romans. Specifically their holiday of Saturnalia, honoring the Roman God Saturn- the God of agriculture. They honored him with a month-long celebration of hedonism and the reverse of societal norms.
In addition to sacrificing, feasting, drinking and general partying the Romans switched up roles by acting as if the slaves and peasants were the top of the crop. They would allow them to sit at the grand banquets and indulge- or overindulge while giving them free reign to speak freely. The courts, schools and businesses were all closed during the holiday so no punishments would be doled out for a slave getting too rowdy. (Though I’m sure that after the celebrations ended those slaves who did go overboard were dealt with harshly.)
In addition, role playing and guising were common forms of entertainment and in this way a peasant might play a king while a king might act as a slave. Another reversal came in the form of gambling which slaves were normally forbidden to do. And finally, one more root of the season- gift giving which took place throughout the holiday.
Fast forward several centuries and Christianity is born. In the beginning Christmas was not part of the Christina calendar- the main holiday of the religious year was Easter. However, many people weren’t giving up their pagan roots and continued to celebrate the winter solstice. So, to help people convert the powers that be adopted the holiday around the same time calling it the birth of Christ (even though all historians agree the man was actually born in summertime.) They took on the decorations, the feasts and the celebratory activities and tied new meaning to all of them.
Looking at the festivities of Saturnalia we can see clear connections to the tradition of 12th Night which was how most people were celebrating Christmas by the middle ages. During 12th night a Lord of Mischief is selected by getting a lucky slice of cake containing a bean. Whoever gets the bean becomes the king and whoever gets the pea becomes queen, ruling over their subjects for the evening. Those subjects, in order to please their king and queen, adapt different roles for their pleasure. Due to this role playing the normal restrictions of being a peasant or servant did not apply and people were free to live it up, drinking tons of wassail, feasting on foods and acting out uproarious roles.
This frivolity continued throughout the Carnival season all the way until Mardi Gras when people went all-out for the last day of excess before the long fast and repentance of lent. The revelers- primarily the poor- became increasingly rowdy during the 12th night carnival, going to the houses of richer socialites and demanding their best food and drink. Those who did not abide them their demands received the worst kind-of mischief. But, just like Lent follows the Carnival so too did those in charge of Christmas observations begin to demand reform of the decadent ways of Christmas.