The somber scene when the Brady siblings and assorted company are up in the middle of the night, eating pies. The scene is funny though because they try to be so serious. There was also "Silent Night" being played in the background and of course Mrs. Brady wakes up feeling that something is wrong.

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Not only that but, how can you be hungry after you eat two or three of Alice's pies.

Wonder who made Breakfast XMass morning, Alice?

Things that make you go "MMMMMMMMMMMMMMMM!"

It's one thing to have all the "hilarious hi-jinks" when they were all kids. But to try to keep it up when they're all adults made them all look absolutely foolish.
Not one of them got any better as actors. Just more forced and stiff.
It was one idiotic exercise in a desperately trying to recapture something that ended permanently about 15 years before. Like going back to high school when you're 33 and trying to be cool.

I don't question the weird things in here. As you said it's The Brady's.
I adore this movie.
So do I. For me, the Brady saga stops with this, because everything seemed to be wrapped up nice and neat by the end of the movie. I really didn't care for the drama and the dark turn of events that happened on "The Bradys" series after this.
And, for being one of my favorite Christmas specials, there really isn't a lot of Christmas imagery to be found on the showwe only see the decorations in the Brady house, and that's about it. No snow, etc. It still gets me in the Christmas spirit, though!!

My sister and I watched this together every year as kids. I then watched it every year with my kids. My kids are now teens and I watch it every year alone.
I don't question the weird things in here. As you said it's The Brady's.
I adore this movie.

When it's time to pick up the kids at the airport, why is Alice the only one running around doing it? She probably had to make a separate trip for each Brady kid and their family.
How did she pick them up if she didn't drive? Did she learn to drive? If she took a cab to get them, why couldn't they just take the cab from the airport to the house and save money? Given that, did she have to use her own money for the cab?
And were they all on a business trip or something? All the Brady kids were dressed to the nines when they got off the plane. And so were Peter and Valerie, who drove in. And they were all dressed up for Christmas dinner, too. Who on earth does that?
I don't know anyone who does that. Especially for a long car ride.

I thought Alice couldn't drive? Also, Alice looked almost all too happy to put her old maid's uniform back on. Alice seemed like she was an indentured servant to the Bradys! Hope they washed her uniform.

If they didn't do these things it wouldn't be the Bradys
You answered your own question.
R.I.P. Rick Ducommun and Tony Longo