fuddle-duddle · verb1
From fuddle, after fuddy-duddy, but development of meaning unclear. Perhaps from the interjection coined by Pierre Trudeau (see next etymology).
fuddle-duddle · interjection2
There is an example of the phrase's use in the early 1940s, in "Mother Finds a Body", by Gypsy Rose Lee: "...when [he] asks me where I was on the night of so-and-so, I'll tell him to go fuddle his duddle". However the expression fuddle-duddle is attributed to Pierre Elliott Trudeau, former prime minister of Canada, who according to some sources said it in parliament on 16 February 1971 and repeated it when pressed by television reporters about using profanity in respect to members of Parliament (Canadian House of Commons).
Etymology from Wiktionary, CC BY-SA 4.0.