When something's qualities can be compared with the relevant use of "poo", an American shortening of "poop". Excreted poop serves no purpose, and smells foul, and though it may look like chocolate, its taste is reprehensible. (Scott, 1975, This Poop Is Not Chocolate)
"This banana is of poo quality"---means the same as "This banana is worthless, its taste may even resemble that of poop."
by Mr.Come&SmokeThatGrassWithMe October 27, 2013