Actually it [the contraction ain't] is still widely used in the rural USA but why it became an upper class British affectation: and still is, baffles me.Jul7ian
In fact ain't did not become "an upper class English affectation". It long served in place of am not I/aren't I? (the latter not strictly speaking grammatically correct although the officially sanctioned form today) and isn't. There is nothing intrinsically wrong with the contraction ain't, which was once used by all classes including the Royal Family, but it fell into disrepute when more people learned to read and found that what was said differed from the written word (which it still often does anyway because of our bizarre way of spelling). The uneducated classes retained ain't, and the upper classes had to say /weistko:t/ instead of weskit for waistcoat, and four-hed for forehead though they had said forred for centuries. (Incidentally I still do).
The nautical terms fo'c'sle for forecastle and sou'wester for southwesterly (the wind and the waterproof mariner's hat) escaped this purge, though you will hear readers on Librivox saying four-ca:s-el too, misled by the spelling.
This is a set of off topic posts from a thread about old bean, old fruit.
It's mostly about ain't, but anyone interested in ain't should check out the WR Dictionary's list of threads HERE.
These posts are mostly about ain't, but in danger of wandering onto yet another tack.