Green’s Dictionary of Slang

absurd, nonsensical.

1868		Western Dly Press 21 Aug. 3/5: The Tories are flapdoodle to induce us to become blind followers of our eminent ‘leaders’.
1878		‘’Arry at the Play’ in Punch 2 Nov. in P. Marks (2006) 40: You know the old flapdoodle muck.
1885		Bulletin (Sydney) 11 Apr. 6/2: He called Queensland, for instance, a flapdoodle country. […] The wisest of these [men] says he was at the banquet seated quite near to the Premier, heard every word distinctly, and is ready to aver that the word used was not flapdoodle, however flattering the expression may be, but flatdoodle, a word of totally different etymology.
1887		Dundee Courier 15 July 2/5: Divsted of all its verbiage, ‘flamdoodle’ compliments, and irrelevant side-issues, his manifesto [etc.].
1888		Sun (N.Y.) n.p.: We wasnt goin to have any high falutin flamdoodle business over him [F&H].
1892		Inangahua Times (N.Z.) 12 Jan. 3/1: This concluded the programme, and an hour afterwards all the flapdoodle orators were snoring.
1902		W.A. Sun. Times (Perth) 26 Jan. 1/1: The lanky legislator’s flap-doodle logic caused even the House messengers to snigger.
1933		Gloucester Citizen 12 Jan. 8/5: Miss Harrison (Durham) condemned as ‘flapdoodle’ schemes the teaching of craft husbandry to villagers.
1990		S. Morgan Homeboy 49: He’d suffered through these flapdoodle attempts at intimidation [...] before.