Green’s Dictionary of Slang

jingle-brains n.

a fool, a dunce.

c.1698		B.E. Dict. Canting Crew n.p.: Jingle-brains a Maggot-pated Fellow.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Jingle brains, a wild, thoughtless, rattling fellow.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1785].
1859		Matsell Vocabulum.
1899		Appeal (St Paul, Minn.) 10 Aug. 3/1: What does old Blunderhead do but detail me, as usual [...] It was just like old Jinglebrains.