It is somewhat facinating that Americans will debate the British origins of many English phrases without ever consulting an Englishman.
A case in point: The debate on the origin of the phase "Rule of Thumb" which people parrot as being a part of British Common Law permitting husbands to beat their wives, which is then used as an explanation as to why it is not written down. A few problems: English Common Law is written down as it utilises past precedent and that the earlist reference to "Rule of Thumb" as an defense for beating a wife in a case near the beginning of the 20th century. The best explanation is this: The phrase has its origins in the textile industry as a way to measure fabrics. Half the circumference of the thumb does approximate an inch. It was well established as a phrase when the English went to the New World. In the Americas, some pious preacher then invented the concept that it was ok to discpline an errant wife whereupon it entered into American folklore. That concept was then exported back to Britian at the turn of the 20th century through literature and by US servicemen who served in Europe.
Another thing which does irk me some is the ancient nursery rhyme which Americans know as "Ring around a Rosie". Here is the version I learnt as a child:

Ring-a-ring o' roses,
A pocket full of posies,
ah-tishoo, ah-tishoo (like sneezing)
We all fall down

It is popular to attribute this rhyme as related to the Black Plague... However another interpretation which is not concidered much is the ancient pre-Christian practice of dancing around the maypole, which is an ancient fertility ritual.
Isn't history so much fun?