Green’s Dictionary of Slang

(US) a fat person, often used as a (usu.) affectionate nickname.

1876		C. Hindley Life and Adventures of a Cheap Jack 147: My first meeting with William Last, alias ‘Tubby,’ was at Brighton.
1887		Wichita Eagle (KS) 17 July 4/3: In picking a ball from the three which were offered, Tubby says, ‘gimme de soft wan.’ Tubby is a batter too.
1890		Sun. Herald (Wash., DC) 14 Sept. 5/2: ‘Tubby’ Dickinson came up with his bat.
1898		‘R. Andom’ Martha and I 217: Tubby Jenkins has been and gone and hypnertised these fellers.
1903		Central Record (Lancaster, KY) 6 Mar. 1/5: ‘Tubby’ Wilkerson, appeared [...] in a cracker-tail coat, doe skin breeches and a bee-gum hat.
1916		‘Taffrail’ Pincher Martin 223: Its beer wot’s done it, Tubby.
1923		‘Sapper’ Jim Maitland (1953) 32: Nevertheless, Tubby, old man.
1934		T. Minehan Boy and Girl Tramps of America (1976) 15: Tubby for God’s sake take a bath.
1952		W.R. Burnett Little Men, Big World 126: Look, Tubby. I got clipped.
1968		G. Cuomo Among Thieves 472: Jo Ann [...] good old tubby-tub that she was, would listen to him.
1979		B. Gutcheon New Girls (1982) 142: No one wants to cuddle with a tubby!
1988		Beano Comic Library No. 145 18: You and um who else, Tubby?
1988		D. Woodrell Muscle for the Wing 11: ‘Man,’ said the shamefaced tubby [...] ‘man, it’s a corset.’.
1990		S. Morgan Homeboy 118: ‘Hey, Tubby!’ called a sharp voice through the sliding glass doors.
1999		K. Sampson Powder 87: They passed two tubbies in grotesque tie-dyed silk.
2022		I. Fitzgerald Dirtbag, Massachusetts 58: I hit Dave Stoll in the face [...] because he called me ‘tubby’.