The story
From a 19th century children's rhyme: "Fatty, Fatty, Boom-a-latty; This is the way he goes! He is so large around the waist, he can not see his toes!". Earliest written attestation from 1899.
Etymology from Wiktionary, CC BY-SA 4.0.
fatty boombalatty
Today it means: An extremely obese person. Full definition →