Green’s Dictionary of Slang

(US) a fat person.

[1593		‘Philip Foulface’ Bacchus’ Bountie in Harleian Misc. II (1809) 308: The eighteenth was one Baudwin Barrelbelly].
1949		R. Mende Spit and the Stars 160: That barrel-ass Johnson is making us memorize about a million of them speeches.
2003		McGill Reed Dict. of N.Z. Sl. 17: barrelarse Short and stubby person.