Though it's Malibu, California, there is 6" of snow on the deck, frost/ice crystals on the windows and it's raining. [EDIT]: It's obvious that the window frost and the snow on the deck are decorative and were put there by Sandy.
When Sandy is explaining that the Donner and Blitzen reindeer figurines are in the wrong order on the piano, Jake can be seen uncharacteristically giggling in one closeup. [EDIT]: It is in perfect character for Jake to be snickering at Sandy and her obsession with Christmas.
When Sandy suggests that everyone sing "The Little Drummer Boy", Jake doesn't even try to. [EDIT]: Jake didn't participate because he had no interest or desire to do so.
Sandy tells Charlie and Alan that the sheets in the dryer are done, then disappears to talk to Berta. She then tells Berta to put some lemon juice on the dryer sheet to really freshen up the laundry. Sandy then appears with the sheets completely folded and ready to put on the bed. Sandy could not have possibly folded the sheets in that short amount of time after briefly talking to Berta.
Given her obsession with Christmas, it is highly doubtful that Sandy would forget to leave milk and cookies for Santa and she most certainly would not have trusted Alan to do it for her.
The writers blow a "teachable moment" that Sandy wouldn't have missed in real life while berating Charlie for switching the order of the reindeer: "Dunner" and "Blixem" were the names Clement Moore originally gave "Donner" and "Blitzen" when he published "A Visit from St. Nicholas" in 1823.