Look, we're not going to razz senior citizens (or immortal holiday icons) for having active sex lives - someday you'll be older too, and you and your partner will make whoopee that will resemble a very rambunctious leather octopus.
But the line "But you probably shouldn't watch it on the sleigh" is more or less wife code for "Please do not pleasure yourself to climax on your mystical toboggan while tearing ass 50,000 feet above the Earth's surface. The headwinds will tear that barber pole in your pants clean off."
Even worse, Mrs. Claus' comment suggests that - at some point during Santa's one-night-only, good-will-fueled delivery of presents to the virtuous tots of the world - Father Christmas has penciled in a masturbation break.
"I am coming to town."
So if Santa's not watching Mrs. Claus' commit acts unspeakable on his Samsung Galaxy III while trying to steer a bunch of supersonic caribou, where is he going to watch this video? At some pay-by-the-hour fleabag? Behind a Carl's Jr. like a drifter aroused by the scent of rancid hamburger meat?
Goodness no, the man has a timetable - a magical timetable. In all likelihood, he's unmasking the turtledove in the sanctity of some of your homes. He does possess the telepathic ability to know when you're sleeping or awake, after all.
"If you just celebrated Hanukkah, you wouldn't have to put up with my shit."