1. Locate a large glass or plastic container. A 32-oz cup should do nicely.
2. Scoop a fairly-large amount of vanilla ice-cream into the cup. (Actually, "scoop" is not the ideal method; the best thing to do is to take a regular teaspoon or tablespoon, then run it across the surface of the ice cream. The idea is to fill the cup loosely, so that there are spaces between the bits of ice cream.)
3. Pour eggnog over the ice cream til the ice cream is covered.
4. Insert bendy-straw. (You can use the straw to stir the concoction, as well; otherwise you'll need a spoon in order to squish everything together.)
5. Drink.
6. Experience bliss.
Merry Christmas indeed!