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?"
"Merry Christmas! Shitter was full!"
"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.