The photo in question shows the celebrity pair looking cozy as they stand next to the North Pole's most famous couple, with Reynolds, 46, noting that Mrs. Claus' name is apparently Jessica and she "smelled like cinnamon buns and sangria."
But there was a major problem Lively, 35, pointed out in the comments: her husband cropped her shoes out of the shot.
"I cropped my wife's shoes out in the photo I posted," the "Deadpool" actor said in a statement posted to Instagram Stories. "It's inexcusable and I'm sorry to anyone I've hurt with this callous lack of fortitude. Heading to the hospital to have my brain weighed."
The "Gossip Girl" alum, who was wearing festive holiday pajamas and a robe in the snap, shared the post to her own Instagram Stories and noted that the shoes were designed by Christian Louboutin.
Lively is currently pregnant with her and Reynolds' fourth child together, having announced the news in September. She and Reynolds, who wed in 2012, are already the parents of three daughters.