Sherlock, contrary to popular belief, loved Christmas. Adored it, even. So many crimes were committed around the holiday.
Judging by the look on John's face, saying that was a bit Not Good.
Seeing as John was already on edge about other . . . incidents, a gesture of some sort seemed appropriate. He attempted Christmas cookies.
Once the smoke detector had stopped going off and he could think again, Sherlock came up with an alternative.
He bought milk. Since it was a present, he stuck a bow on it, complete with a tag.
John was so surprised at the milk that he didn't notice the mold culture that was also in the fridge, so Sherlock counted it as a win.
The . . . curiously warm feeling John's gift to him gave him demanded further study. Until then, he would simply enjoy the new shock blanket.