When you work your way down to the lowest form of humor, you reach the scatological…
Wikipedia has a great description of it under the other appropriate heading: “Toilet Humor”.
And of course, A Game of Porcelain Thrones is ALL about toilet humor.
If it’s good enough for Chaucer, it’s good enough for me!
Toilet humour or scatological humour is a type of off-colour humour dealing with defecation, urination and flatulence, and to a lesser extent vomiting and other body functions. It sees substantial crossover with sexual humour, such as dick jokes. The term scatology is derived from the word ‘scat’ often interchanged with ‘feces’ particularly when referring to droppings of prey animals while hunting. (i.e.bear-scat) From the Greek skor, skat.
Toilet humour is popular among a wide range of ages, but is especially popular with children and teenagers, for whom cultural taboos related to acknowledgement of waste excretion still have a degree of novelty. The humour comes from the rejection of such taboos, and is a part of modern culture.[ Examples can also be found in earlier literature, including The Canterbury Tales by Geoffrey Chaucer.
Of course, if you can’t take my word for it or Wikipedia’s word, take it from one of the greats: