Don’t say pigf***er in front of Jesus. (The Spirit of Christmas)
If the condemed soul of a long-dead Roman emperor shows up at your house intent on murdering you as part of a conspiracy cooked up by Haman, Ivan the Terrible, Caligula, Simon Legree, and Lucretia Borgia, he can be turned into a lifelong friend with the offer of food, drink, and a thoughtful present. (The Plot to Overthrow Christmas)
You can put your eye out with a BB gun. (A Christmas Story)
Santa Clause is divorced and has a child-The Santa Clause
Only the threat of death and an unkept grave will give you the true Christmas Spirit, even if you think you are too old to change.-- A Christmas Carol
Eating a policeman’s Whistle will only have comical consquences–Frosty The Snowman
If you’re a poor, neglected, but warm-hearted little kid, you can almost guarantee someone will somehow make all of your Christmas dreams come true.
(I’ve always wondered how many impoverished kids watch these shows and expect their own Christmas Miricle, and are embittered when one doesn’t manifest.)
Be very careful with a triple-dog dare. (A Christmas Story)
I wouldn’t necessarily say this is specific to Christmas specials. I consider this one of the rules of comedy physics.
No matter how nasty and mean spirited you are you have to act nice simply because it’s Christmas Eve and/or Christmas. (A Christmas Carole and every stupid pastiche based on it.)
No matter how noble minded your production, how scintillating your plot, how skilled your writers and actors, just about anyone can make a movie or TV special that is unwatchable crap.
Chinese restaurants in small midwestern cities are open on Christmas day, presumably because their owners are too culturally ignorant to realize that 99% of their potential customers will be having dinner at home that day (and it would thus be unprofitable to open). (A Christmas Story)
2nd-graders have significant portions of the King James Bible comitted to memory. (Charlie Brown)
When adults speak to children, they sound like off-key trumpets. (Charlie Brown)
You’re determined nice or evil based on whether you give someone a VCR or a towel. (Scrooged)
Mrs. Claus is an idiot.
With a couple of socks on its antlers, a reindeer can pass for a dog.
It’s not weird to invite a strange old man with a cold into your hosue and sing a song with him.
The Year Without a Santa Claus
Mrs. Claus is apparently Jewish, and Santa himself is a bitter old man who could be a poster boy for Weight Watchers.
Rudolph the Red-Nosed Reindeer
Awww, Zoggie, I was about to point out that Mrs. Claus is Jewish.
Four kids using ping-pong balls and soap bubbles can take on the Evil Overlord of Mars, who is armed with a disintegration ray, and win.
–Santa Claus Conquers the Martians
Aww. Ain’t I a stinker? 
Gosh, I’m sorry, Dangerosa. I actually realized that myself from reading the Rudolph thread from a couple of years ago.
Another something I learned:
Occasionally, even Santa uses the doorbell.
Toddlers wonder about what to get one another for Christmas.
Rugrats
And from all of them: The Gift of the Magi will NEVER ever get old.