muffin baker, n. — Green’s Dictionary of Slang

muffin baker n.

[rhy. sl. = quaker n.; orig. misunderstood by Hotten and entered in early edn as a ‘Quaker’ in religious meaning]

excrement when hard and retained.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict. 367: Muffin baker, a Quaker (slang term for excrement).
1960		J. Franklyn Dict. of Rhy. Sl. 97/2: muffin baker A quaker [...] applied to excrement.
1984		Partridge DSUE (8th edn) 764: A ‘quaker’ in the Cockney low s. sense, for excrement long retained.