I've got a couple experiences...arriving in Colombia on Dec 25, not super relevant, because they celebrate Christmas on the 24th. Obviously the airports are decorated and the FAs make happy holiday type statements but nothing special on board.
Working under WS as a contractor for 6 years, there were a few great days to work. Sep 11, Friday the 13th (any month) and Christmas day. Those days the loads were LIGHTTTTTT. The Sep 11 thing wore off, I worked there from 06-13, by 08-09 people were fine with flying on 9/11 again. I got to work on a Friday and for the life of me couldn't figure out why there was so few people...my only deduction...bad luck, Fri the 13th. I kept track going forward and it persisted.
Christmas day was another ball of wax. Being at YVR, there's not many arriving red eyes, but our red eyes going OUT on Dec 24 were full. So maybe YYZ was super busy. Our flights to HNL/OGG/LAS on Dec 25 I recall being super busy but not busier than the rest of the season. Dec 26 everything is back to normal. Best time to work is probably Dec 25 on the 1600-2430 shift, outbound loads were usually light, inbound loads even lighter.
WS did a gift giving thing I'm sure you guys have seen the video it's from a couple years ago. I can't go on youtube at work, but if you haven't seen it, search WestJet santa flight maybe? I laughed hard when the guy who asked for socks/underwear got them, meanwhile someone else got a huge tv lol.
What I'd like to see, maybe on a couple flights, a turkey dinner! I'm not even a huge fan, but I think an airline could do a couple surprise flights and have a turkey dinner, even if it wasn't international. It seems like something WS might do...or a full service airline could do it with some coordination from catering on an international flight.
Flying at/around Christmas is great imo, I like that most people are in a decent mood, almost everyone is either going on vacation or to see family, I hate the music but I like the decorations. The airports are busier, but often the traffic isn't so I like that too.