Green’s Dictionary of Slang

1. of a person, despicable, repellent.

1745		A. Hamilton Tuesday Club Bk II in Micklus (1995) 28: They would call him a hundred abusive names [...] such as lousy, scabby scot, poor rascally pedlar, Itchified son of a bitch [...] Skip kennel Scrub, nasty, blewbellied, blanket ars’d, hip-shotten, maggot eaten, round about, Snuff besmeard, flyblown Son of a whore.
1925		J. Stevens ‘Logger Talk’ in AS I:3 139: Holy old blue-bellied, bald-headed, Jesus H. jumping old mackinaw Christ!
1929		E. Caldwell Bastard (1963) 35: I’m looking for that blue-bellied bastard.

2. (US, Southern) pertaining to a Northerner, esp. a New Englander.

1863		J.J. Geer Beyond the Lines 90: They saluted us with such epithets as ‘blue-bellied Yankees’ and ‘dirty nigger-thieves’.
1866		C.H. Smith Bill Arp 46: Did you suppose it was going to take a year to whip a parcel of blue-bellied Yankees? They knew who was coming after their codfish.
c.1880		E. Pierrepoint Speeches 6: This being the case, let us take one [i.e. a Northerner] who is less ‘blue-bellied’ than the most of them.
1893		R.G. Hampton Major in Wash. City 56: There’s that Gresham, who was a blue-bellied Abolitioner.
1914		J.C. Ruppenthal ‘A Word-List From Kansas’ in DN IV:ii 103: blue-bellied Yankee, n. An out and out New Englander. ‘My mother was a German from North Carolina but my father was a blue-bellied Yankee’.
1933		(con. 1860s) R. Bradford Kingdom Coming 164: It was just a matter of time until old Abe Lincoln would be pulling in his horns, the damned old blue-bellied nigger-lover.
1944		(ref. to Civil War) J.S. Pennell Hist. of Rome Hanks 42: We’ll show the fourflushin’ bluebellied sonsuhbitches.
1985		(ref. to Civil War) Tom Petty ‘Rebels’ 🎵 I can still feel the eyes of those blue-bellied devils.