When Carl gives Homer a DVD player and the first season of ''MagnumPI'', Homer forgets that he is Lenny’s “Secret Santa”, so he hastily gives him Certs. Also, Mr. Burns gives everyone a caferteria voucher as a Christmas bonus, except Homer, who gets a Joe [=DiMaggio=] baseball card (which, him being Burns, believes is worthless - Burns is so outdated he thinks [=DiMaggio=] is a rookie and Homer's surprise was about the fact they "started" to allow ethnics in the big leagues)). Homer trades it in to Comic Book Guy, who gives him everything in his register. With this small fortune, the Simpsons go Christmas shopping and Homer promoses to spend his money on a huge Christmas tree, but instead squanders it on a personalized talking astrolabe. When his family finds out, they call him out on his selfish act, with Marge saying that he doesn't care about anybody but himself. What’s worse is that Homer can’t return the astrolabe as the astrolabe itself reminded him after Homer was called out for his selfishness.

Later that night, Homer watches ''Mr. [=McGrew=]’s Christmas Carol'' and sees the Scrooge-type character doomed to go to Hell because of his selfishness. Fearing the same might happen to him, Homer decides to change his ways and become the nicest person in town. Around town, Homer performs good deeds for Springfield’s citizens, including giving his old clothes to charity, giving Lenny a photo cube, giving Marge the last pork chop at dinner and building a skating rink in his backyard. This kind attitude of Homer’s causes resident nice guy Ned Flanders to get jealous and so he competes buy dressing up as Santa and giving everyone in town a free gift and renting his house to a fraternity. Homer decides to get back by buying everyone a new car, but Lisa tells him that as a Buddhist, she believes there’s too much commercialism in Christmas and that everyone is better off without presents.

Inspired, Homer decides to to the “ultimate good deed” by stealing Christmas. That morning, as Homer prepares to burn the stolen gifts in a bonfire, an angry mob shows up. But Homer manages to calm everyone down by showing them a Christmas star in the sky (actually a flare from Hans Moleman). Homer gives back the gifts and everyone joins in singing a Christmas carol, including Moe after once again attempting suicide.
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!!"'Tis the Fifteenth Season" contains examples of:
* ArtShift: The Simpsons watch an {{expy}} of the California Raisins, with the special animated via claymation.
* ContinuityNod: Lisa reminds Homer that she's a Buddhist after converting in "She of Little Faith".
* DrivenToSuicide: Moe, as per every Christmas, attempts and fails to commit suicide at the end.
* ExiledToTheCouch: Homer sleeps on the couch at night after angering his family with his selfishness.
* EyeScream: Homer gives Lenny a photo cube with the edges trimmed so Lenny won't jab the points in his eye.
-->'''Lenny:''' Now it only hurts a little.
* HowTheCharacterStoleChristmas
-->'''Homer''': You're a smart one, Homer J.,\\
You're as crafty as a skunk.\\
You'll make everybody happy when they're rid of Flanders' junk,\\
Homer Ja-a-ay.\\
I'd call you a double bacon genius-burger,\\
And just a little drunk!
* HeelRealization: Homer watching a Christmas special on TV makes him decide to be a better person.
* {{Hypocrite}}: Lisa tells Homer about how she feels that Christmas would be better without all the materialism and commercialism. She is later shown among the mob wanting to kill Homer for taking their stuff.
* InstantSedation: While Homer is stealing Christmas, he is spotted by baby Gerald (a la Cindy Lou Who), so he knocks him (and his teddy bear) out with a chloroform rag.
* LimitedWardrobe: Homer is shown donating his old clothes to the needy. Cut to hobos waring white shirts and blue pants.
* LoopholeAbuse: The place where the Simpsons go Christmas shopping has the following slogan: "Our prices discriminate because we can't"
* RightBehindMe: To give an example of somebody more selfish than him, Homer started describing Mr. Burns, who overheard him. [[SubvertedTrope Fortunately]], Burns thought Homer was talking of a woman named Kathy, who ''does'' look like Burns except for the fact she's a woman.
* ShoutOut
** Homer watches ''[[WesternAnimation/MrMagoo Mr. McGrew's Christmas Carol]]''
** Homer tries to [[Literature/HowTheGrinchStoleChristmas steal Christmas]]
* ToTheTuneOf: "You're a smart one, Homer J."
* WellIntentionedExtremist: Homer tries to get rid of the excess commercialism of the holidays by stealing all the presents and decorations in town and burning them. Naturally, it just pisses everyone off.
* YetAnotherChristmasCarol: Lisa shows Homer that many adaptations of ''Literature/AChristmasCarol'' exist, showing scenes from Christmas episodes of ''Franchise/StarTrek'' and ''FamilyMatters''