When you defecate down someone's chimney and wait for them to turn their fireplace on, to the smell of a burning boulder.
Commonly done at Christmas time.
Daniel: Holy shit, do you smell that?
Florence: Yeah, looks like someone's given you a Christmas Pudding, probably Santa.
Feces found in adult diapers of an old person after digesting a fruitcake, which may still have the red and green candied cherries in it, resulting in a colorful festive "pudding".
Missy had to change Mr. Jone's Depends after he soiled himself, only to discover it full of "Christmas Pudding". She saved it as a gag pinata for her blind Mexican friend.