Laura, of course it is a tradition, but for many people it is really strange and not very appropriate for  the Christmas crib, even for some catalan people I know. In my oppinion I find it funny, but I have never added this figure at home. Being a tradition doesn't mean everybody likes it. 

for me, "El tió" is different, nobody shows its intimate parts to anybody and it is really funny when receiving gifts after hitting the trunk of a tree.

Best regards. 

They are a part of my culture (traditions) and I've "lived" them since I was born.

I was thinking about the "Caganer" (the figure of the manger) and the "Caga tió" (the poop log), which have their origin and their meaning. 

Laura and Torusan, thanks for your comments. 

Maybe many people wouldn't like this tradition which, in my opinion, is too irreverent.

Too funny! In Provence, I bought a Mistral santon, which is their regional figurine for the crèche. Now, I'm thinking that I should collect all these regional figurines. It would make for a truly eccentric nativity scene! :)

I have enjoyed this video about the six craziest traditions :)

I can't say anything else apart from pointing out that we, Catalans, are so scatological in Xmas!