Green’s Dictionary of Slang

1. (US) foolish.

1927

D. Hammett ‘The Big Knockover’ Story Omnibus (1966) 284: He was jingle-brained, of course, and needed holding.

2. (also jingle) intoxicated.

1935		A.J. Pollock Und. Speaks n.p.: Jingle, intoxicated.
1999		J. Baker Walking With Ghosts (2000) 182: I’m jingle-brained with dope and goofy about this woman here.