It doesn't take the crew of the enterprise long to figure out that Scotty is really into the festive season that is Christmas. Starting from the first of what was traditionally called December (before the move to standard) right up until new years day Scotty is in a perpetually cheerful mood. The Christmas cheer quickly spreads around the ship as a result of Scotty's enthusiasm. It doesn't take long for him to arrange for the Enterprise to be decorated garishly with sparkly tinsel, plastic reindeer and chubby Santas. A quick raid of Sulu's greenhouse results in the ship being decked out head to toe with mistletoe dangling from almost every doorway and turbo lift. There would have been enough to cover every door way, had Keenser not eaten a large portion of the decorations before Scotty caught him.
The icing on the cake is of course the tree which is a blaze with flashing lights and smothered in ornaments and candy canes in what was once the mess hall but has now been transformed into Santa's grotto. When Scotty is not down in engineering belting out popular Xmas hits he can be found there wearing an authentic Santa suit, asking fellow crewmembers if they have been good this year and what they want for Christmas. He is of course assisted in this task by Keenser who has stepped up to the role of Christmas elf. While Spock is the more obvious candidate he is also reluctant to wear the stripy tights and silly hat for reasons other than being Jewish.
However that doesn't prevent him from indulging in a few of the cookies, cakes and puddings Scotty bakes for everyone. Indeed Spock is soon particularly partial to the mince pies, having been assured by Scotty that they are in fact meat free. Scotty is such a good baker that it isn't long before more than half the crew have to double their exercise regimes in order to compensate for all the extra calories they are consuming.
Christmas day itself is a whirlwind of presents and torn wrapping paper and noise and excitement that starts early, well before Spock has meditated. Somehow Scotty manages to prepare a roast Christmas lunch for every crew member with lashings of cranberry sauce and plenty of alcohol. Crackers are pulled and jokes exchanged, with everyone including McCoy enjoying themselves. Later on once the excitement has finally begun to die down Chekov falls asleep, while everyone else is sitting down to watch a Christmas message from Admiral Pike. Uhura patiently sits letting him rest his head on her lap as she watches the bridge team play Monopoly. He wakes up in time to catch the ending of the Christmas film but remains besides Uhura cuddling cutely, with Uhura stroking his head like his mother back in Russia loved to.
Keenser having found a chair to climb on, quickly gets drunk on the remainder of the mistletoe and is helped to bed by Scotty least he cause a scene. Strangely Scotty doesn't return to the party, nor is he seen again until well after Boxing Day.