Clark: Where do you think you're going? Nobody's leaving. Nobody's walking out on this fun, old-fashioned family Christmas. No, no. We're all in this together. This is a full-blown, four-alarm holiday emergency here. We're gonna press on, and we're gonna have the hap, hap, happiest Christmas since Bing Crosby tap-danced with Danny fucking Kaye. And when Santa squeezes his fat white ass down that chimney tonight, he's gonna find the jolliest bunch of assholes this side of the nuthouse.
In the scene where Clark is working on the lights the full moon is shown. This is December 14th according to the advent calendar. On December 24th when Santa's sleigh goes sailing over the moon, it is still full.
After Eddie's arrival, he and Clark are in the living room, drinking eggnog out of mugs shaped like moose heads. The original "Vacation" was all about the Griswold's getting to the fictional theme park Wally World, whose mascot is a moose named Marty.