Danielle Mead Skjelver wants to tell you all about it. You can find an entire paper authored by her on Luther’s scatological expressions at German Hercules: The Impact of Scatology on the Definition of Martin Luther as a Man 1483-1546.
Apparently in medieval and Reformation Germany, poop jokes made you more manly.
Introduction: The writings of Martin Luther are among the most studied in the world. With words sublime, he gave the Christian God back to the common man, and yet Luther also spoke with shocking cruelty and vulgarity. Martin Luther’s employment of vulgarity, and specifically scatological vulgarity, in his writings and speech has drawn criticism, embarrassment, and accusations of psychological instability. But there was power in coarse language, for Martin Luther’s combative use of scatology defined him as a virile male in sixteenth century Germany. Brash and full of bravado, the scatology of Martin Luther lent him the appearance of fearlessness. Scatology in many societies is associated with the beer hall and the military, two bastions of masculinity (analogous to today’s ‘locker-room talk’). Even among elites in the Europe of Luther’s day, scatology was not unusual. This was particularly true in German speaking lands. In a time of strong proto-nationalism, his combative and demeaning brand of scatology, which was leveled against not only a spiritual but also a foreign enemy in the Papacy, secured for him the definition of virile German male. In spite of his emaciated condition from years of fasting, and later in life in spite of corpulence, and even in spite of his public proclamations that he proudly helped his wife wash diapers, Luther was ever the man in the eyes of both allies and enemies. His virility was largely the product of his aggressive use of scatological language, for in demeaning his enemies, Luther diminished their virility. His adversaries, however, vilified his character in such a way that their attacks emphasized Luther’s masculinity.