Clark and Ellen singing at the beginning, while Rusty and Audrey are less than enthusiastic.
Clark: Take it, Russ! (Russ stays silent while Clark and Ellen Bob their heads in rhythm to the unsung phrase)
Clark and Ellen:: ...fa la la la la, la la la la!
"Dad, did you bring a saw?" (loud timpani cue, then it cuts to the Griswalds driving home with the tree HUGELY uprooted on top of the car with "Oh Come All ye Faithful" playing in a "wah wah wah waaaaah" style)
"Merry Christmas! Shitter was full!"
The epic rant after Clark doesn't get a Christmas bonus:
Clark: Hey! If any of you are looking for any last-minute gift ideas for me, I have one. I'd like Frank Shirley, my boss, right here tonight. I want him brought from his happy holiday slumber over there on Melody Lane with all the other rich people and I want him brought right here, with a big ribbon on his head, and I want to look him straight in the eye and I want to tell him what a cheap, lying, no-good, rotten, four-flushing, low-life, snake-licking, dirt-eating, inbred, overstuffed, ignorant, blood-sucking, dog-kissing, brainless, dickless, hopeless, heartless, fat-ass, bug-eyed, stiff-legged, spotty-lipped, worm-headed sack of monkey shit he is! Hallelujah! Holy shit! Where's the Tylenol?
When Cousin Eddie first arrives, he touches one of the decorations scattered around the house, and everything on it immediately shatters off.
While out shopping, Clark puts some lightbulbs on his shopping cart, which are crushed by the enormous bag of dogfood Cousin Eddie puts on top of them not a second later. The fact that neither of them notice it at all is just awesome.
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!