If you're curious to know more about this festive drink, take a few points from Mental Floss, with a pinch of nutmeg.
And just in case you're planning to make some, here's a recipe from the same site you may want to try:
Recipe courtesy Alton Brown, 2012
Alton Brown’s Nog of Ages
12 large chicken eggs (see note)
1 pound sugar
1 pint half n half (see the other note)
1 pint whole milk
1 pint heavy cream
1 cup jamaican rum
1 cup cognac
1 cup bourbon
1 tsp freshly grated nutmeg (plus more for serving)
1/4 tsp kosher salt
• Separate the eggs and store the whites for another purpose
• Beat the yolks with the sugar and nutmeg in a large mixing bowl until the mixture lightens in color and falls off the whisk in a solid “ribbon.”
• Combine dairy, booze, and salt in a second bowl or pitcher and then slowly beat into the egg mixture.
• Move to a large glass jar (or a couple of smaller ones) and store in the fridge for a minimum of 2 weeks. A month would be better, and two better still. In fact, there’s nothing that says you couldn’t age it a year but I’ve just never been able to wait that long.
• Serve in mugs or cups topped with a little extra nutmeg grated right on top.