what's the idea

what's the idea

Also, what's the big idea; the very idea. What do you think you are doing? What foolishness do you have in mind? For example, What's the idea of taking the car without permission? or You've invited yourself along? What's the big idea? or Take a two-year-old up Mount Washington? The very idea! These phrases, all implying the speaker's disapproval, use idea in the sense of "what one has in mind." The first two date from about 1900; the third is heard more in Britain than America.
See also: idea
References in classic literature ?
Directly I saw you--see here, what's the idea of this road-work?
Richard Protheroe - Summer Vibes What's the idea behind the Summer Vibes Festival in Merthyr?
I mean what's the idea with this walking out of class in opposition to the war?
And what's the idea of unloading it out there on the lawn?