Green’s Dictionary of Slang

a parson, ‘who at least once a week abuses his best benefactor, i.e. the devil’ (Grose 1785).

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Ungrateful man, a parson, who at least once a week abuses his best benefactor, i.e. the devil.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1891		Tuapeka Times (Otago, NZ) 12 Aug. 6/4: Clergymen are called the ‘ungrateful man’’.