knight and barrow pig, n. — Green’s Dictionary of Slang

knight and barrow pig n.

[i.e one who poses as a knight, but is more of a barrow-pig, i.e. a (castrated) pig; note phr. more hog than gentleman]

someone with ideas above their station.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Knight and barrow pig, more hog than gentleman, saying of any low pretender to precedency.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1785].