A Christmas' Gift. (Scatological of course)

In Catalonia traditional Christmas decorations consist of a large model of the city of Bethlehem. The caganer is a particular feature of modern Catalan nativity scenes. Accompanying Mary, Joseph, Jesus, the Shepherds and company, the caganer is often tucked away in a corner of the model, typically nowhere near the manger scene.
Possible reasons for placing a man who is in the act of excreting waste in a scene which is widely considered holy include:
Tradition.
Perceived humor.
Finding the Caganer is a fun game, especially for children.
The Caganer represents the equality of all people: regardless of status, race, or gender, everyone defecates.
Increased naturalism of an otherwise archetypal (thus idealised) story, so that it is more believable, taken literally and seriously.
The idea that God will manifest himself when he is ready, without regard for whether we human beings are ready or not.
The caganer reinforces that the infant Jesus is God in human form, with all that being human implies.
Originally, the Caganer was portrayed as a Catalan peasant wearing a traditional hat called a barretina — a red stocking hat with a black band. The caganer is not the only defecating character in the Catalan Christmas tradition, another is the Tió de Nadal, which also makes extensive use of the image of human waste production. Other mentions of feces and defecation are common in Catalan folklore, indeed, one popular Catalan phrase before eating says "menja bé, caga fort i no tinguis por a la mort!" (Eat well, shit strong and don't be afraid of death!).


A more comprehensive description can be found here