At the drop of a hat

This expression of American origin meaning to do something in an instant, suddenly and spontaneously, is first cited in this sense from 1837. The dropping of a hat used to be the signal for starting foot or horse races and also brawls, especially in the American Wild West. In all such instances, the dropping of a hat signalled immediate action of some sort or other and some sources maintain this is where the expression came from. On the other hand, the dropping of a hat only takes a second or two in any environment and, indeed, this is reflected in the 1837 citation put forward by Michael Quinion: http://www.worldwidewords.org/qa/qa-att1.htm “They could agree in the twinkling of an eye - at the drop of a hat - at the crook of a finger - to usurp the sovereign power; they cannot agree, in four months, to relinquish it.” Register of Debates in Congress, 12 October 1837. At the drop of a hat is clearly being used here as an American synonym for ‘in the twinkling of an eye’ and ‘at the crook of a finger’. So perhaps that is all it was ever meant to be.