Green’s Dictionary of Slang

a fool, a simpleton.

1673		T. Shadwell Epsom Wells IV i: mrs. bisk: Where have you been, you Fop Doodle? bisk: What’s that to you Jilt-Flirts?
1689		T. Shadwell Bury Fair V i: Come come, you brace of Fopdoodles.
1830		N. Devon Jrnl 8 July 4/5: Sir Frederick Fopdoodle.
1850		E.V. Kenealy Goethe: a New Pantomime in Poetical Works 2 (1878) 337: Meacock, Buzzer, poor Fopdoodle / You're a pretty first floor lodger!
1859		‘Non-Sucker’ [Henry Shutts] Tobacco 25: Your empty, idle, popinjay fopdoodles.