One expression of sadism concerns itself with humiliation, and the humiliation of the main character as a source of gratification for the reader was a recurring motif. (As with the themes of urine and diapers, the only laughter would be that of the delighted deviant.)
Of course, a sadist who drew delight from the humiliation of others and who only imagined sadism as a disorder of finding gratification in the infliction of physical pain or of physical discomfort might not recognize the appropriateness of the label for his or her own sadism. Alternately, someone might be so mind-blind as to miss the theme of humiliation.
The series had ten chapters, the first seven of which had urine jokes. Someone cannot do basic arithmetic.