Pour about 2/3 of the container of eggnog in a shallow glass dish, cover with plastic wrap and place in freezer. When it is frozen, it will be sort of a like sherbert. Scoop half of this frozen eggnog into a blender pitcher.
Add liquors and blend. Then add enough of the unfrozen eggnog until you get a nice smooth slushy texture. If you want it stronger, add more liquor and less of the unfrozen eggnog.
I like to top mine with whipped cream and sprinkle with a cinnamon/sugar mixture.
For a non alcoholic version, replace liquor with more unfrozen eggnog. Also, you may wish to thin it out with milk or cream. Freezing lowered the intensity of flavor, so when I added the cream, I needed to also add a little sugar and a little nutmeg.
Unused frozen eggnog can be transferred to a freezer dish and kept in the freezer for a quickie drink anytime. Yummy!