Green’s Dictionary of Slang

flapdoodle n.2

also doodleflap, flamdoodle
[ety. unknown; the image is of flapping lips]

1. [mid-19C+] nonsense, rubbish; thus flapdoodler n., a charlatan, a politician, a speaker of portentous but empty words; also as v..

2. [1920s] (US) any thing.

3. [1950s] a fuss, an uproar.