Green’s Dictionary of Slang

(orig. US) more a threat than a question, usu. asked when someone is doing or saying something of which the speaker disapproves.

1912		Ade Knocking the Neighbors 169: ‘What is the Idea?’ asked the alcoholic Henchman, looking vainly about.
1917		R. Lardner Gullible’s Travels 83: Then we done a little spoonin’ and then I ast her what was the big idear.
1920		Ade Hand-made Fables 55: One day when the True Friend had Condoled until she was sniffing on the Verge of Hysteria, Joe walked in on them and wanted to Know what was the whole Idea.
1922		M. Bodenheim ‘Poetry’ in Introducing Irony 70: S-a-a-y, what’s the idea?
1923		Wodehouse Leave it to Psmith (1993) 515: What’s the big idea?
1929		J. Lait Broadway Melody 73: ‘What’s the big idee?’ he shot at her. ‘I was on there downstage goin’ through my number, an’ here you were, holdin’ hands with that tailor-made bum.’.
1938		X. Herbert Capricornia (1939) 526: You can’t lock him up. What’s the idea?
1939		J. Weidman What’s In It For Me? 204: Then what’s the big idea making a proposition at like that?
1940		J.G. Brandon Gang War 122: What’s the bright idea, if any, in this particular move.
1949		N. Algren Man with the Golden Arm 75: The dummy pinched me, Frankie — what’s the big idea?
1957		R. Prather Always Leave ’Em Dying 37: ‘Watch it, mister,’ I said. ‘What’s the idea?’.
1957		D. Niland Call Me When the Cross Turns Over (1958) 75: What’s the big idea, coming to bludge on us?
1960		J. Iggulden Storms of Summer 97: ‘What’s the big idea you bastards working so close to me,’ roared Harry.
1960		‘Nino Culotta’ Cop This Lot 197: You blokes’re done up like sore fingers. Wot’s the idea?
1976		P. Theroux Family Arsenal 273: You got me out of bed this morning. What’s the big idea?
1987		M. Bail Holden’s Performance (1989) 253: ‘What’s the big idea?’ He turned to Harriet. ‘What’s going on?’.