Green’s Dictionary of Slang

a fool, a gullible person.

1569–70		T. Preston Cambyses B3: Gogs hart slaue dost thinke I am a sixpeny Jug: No wis ye Jack I looke a little more smug.
1672–80		‘The Citizen’s Vindication’ in Ebsworth Roxburghe Ballads (1891) VII:2 278: Match but a Bum[p]kin to a man, or Juggs to London Lasses, / And then distinguish, if you can, how Londoners surpasses.
1705–07		N. Ward Hudibras Redivivus II:2 24: All Country Jugs, with Sun-burnt Faces, / Brown Joans, and Wainscot-colour’d Lasses.
1729		Hell upon Earth 8: A general Jumble and Jostle [...] of Country Juggs, Barbers ’Prentices, Tavern Drawers [etc].
1887		‘’Arry on His Critics’ Punch 17 Dec. 280/1: The mugs and the jugs never joke, / Never gag, never work in a wheeze.
1892		E.J. Milliken ’Arry Ballads 63: Bell’s a bloomer, and, Jack thought, a bit of a jug.
1956		H. Gold Man Who Was Not With It (1965) 96: It was nice to find the born jug of the continent.