Green’s Dictionary of Slang

1. nonsense, or one who talks nonsense.

1897		O. Wister Lin McLean 131: Well, I don’t say my prayers any more. I told Mr. Perkins [...] I think he is a flubdub anyway.
1917		F. Packard Adventures of Jimmie Dale (1918) I iii: She’s crazy on this society stunt—all flubdub to me of course.
1920		Ade Hand-made Fables 325: But they had to keep posted on all this Flub.
1922–24		O.O. McIntyre White Light Nights 49: There is little flubdubbery among the ‘ivory benders’. [...] Any number of them have never had a music lesson.
1929		M. Bodenheim Sixty Seconds 22: All the rest was flubdub, preacher’s lies.
1934		N.Y. Times 20 Oct. n.p.: It is Baghdad without the melodramatic flubdub.
1944		H.B. Hersey G.I. Laughs 56: The corporal says ‘flub dub’.

2. (US) a foolish mistake.

1981		Graziano & Corsel Somebody Down Here Likes Me, Too 97: Sure, I make flubs.
2008		Tampa Trib. (FL) 1 May 2/1: [headline] Everybody’s Talkin’ About Abdul’s Latest Flub [...] Watching Abdul self-destruct is great sport for some.