Although I knew that he had spent a lot of time sitting on the toilet, I wasn't quite aware of how much he referred to poop and scatological matters generally in his writings and sermons, so I went looking for more information.
And here's what I found: a pretty interesting research paper from 2008 that looks at the question of why Luther engaged in scatological expressions so much. This has, apparently been the subject of much academic attention over the years, and the paper summarises the various schools of thought, before concluding that, in the context of German culture at the time, throwing literary "shit" at his enemies gave him the desirable air of virile masculinity.
It would seem that Germans have always had a scatological bent - I'm sure someone has had a go at explaining that, but I'll go looking for that another day. This part notes the way poop was used in disputes at the time:
Ain't history grand?
(As an aside, this description of Luther's eyes is of interest:
Seems a good lead for a science fiction story based on his being a robot; but I guess all of the sitting on the toilet suggests a design fault.)
Reading about this reminds me that the other great nation with an unusual degree of interest in poo is Japan. I'm sure there must be lots of material on the net about this, but here's a short-ish but useful essay on the topic.
I may well have noted this unusual connection before: why do two nations so far apart have this in common? Like the esoteric stories of Jesus travelling to India (or Japan), was there a prophet of digestive health who travelled from Germany to Japan in the first millennium AD, proselytising the importance of having well formed poo, but who remains mysteriously unrecorded in history?
Just a thought for someone's future research endeavour.