Green’s Dictionary of Slang

a stupid person.

1969		J. Scanlan Davis 109: The one-star fuzz-brains who would crush Hitler with cocktails [HDAS].
1986		S. King It (1987) 354: Oh, Richie, you’re such a fuzzbrain.
1999		S.E. Stevens ‘The Shock of the Familiar’ 7 May at Salon.com 🌐 Some failed his first test. ‘Do periodicals count?’ one fuzzbrain inquired.