Green’s Dictionary of Slang

(US) to an overwight individual, a cynical term of address.

1960		‘Lord & Marshall’ So Willing 42: That was the thing with girls, particularly short fat ugly girls like the two who came along to share the coke. [...] It was obvious that Della preferred to go off with him, rather than hang around with the tons of fun.
1981		H. Gould Fort Apache, The Bronx 179: Murphy shoved him back. ‘Sit down tons of fun, and don’t try to tell a cop what to do.’.