"one who is crazy," 1940, from earlier adjective (1935), from noun meaning "the sound of little bells" (1894), ultimately imitative of the tinkling sound (by 1848; see ding (v.)). The extended senses are from the notion of hearing bells in the head.
1570s, "consisting of flakes," from flake + -y (2). Meaning "eccentric, crazy" first recorded 1959, said to be American English baseball slang, but probably from earlier druggie slang flake "cocaine" (1920s). Flake (n.) "eccentric person" is a 1968 back-formation from it. Related: Flakiness.
The term 'flake' needs explanation. It's an insider's word, used throughout baseball, usually as an adjective; someone is considered 'flaky.' It does not mean anything so crude as 'crazy,' but it's well beyond 'screwball' and far off to the side of 'eccentric.' [New York Times, April 26, 1964]
from the title of Joseph Heller's 1961 novel. In widespread use only after release of the movie based on the book in 1970. The catch (n.) is that a bomber pilot is insane if he flies combat missions without asking to be relieved from duty and thus is eligible to be relieved from duty. But asking to be relieved from duty indicates sanity and thus he must keep flying missions.
There was only one catch and that was Catch-22, which specified that a concern for one's safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions. Orr would be crazy to fly more missions and sane if he didn't, but if he was sane he had to fly them. If he flew them he was crazy and didn't have to; but if he didn't want to he was sane and had to. Yossarian was moved very deeply by the absolute simplicity of this clause of Catch-22 and let out a respectful whistle.
"That's some catch, that Catch-22," he observed.
"It's the best there is," Doc Daneeka agreed.