Do you ever wonder where certain sayings came from? The “real McCoy” is used to mean, an authentic item, not a fake or a copy. But where did it hail from, you may ask.
“The real MacKay,” is a Scots phrase that first appeared in print in 1856 as “A drappie o’ [drop of] the real MacKay,” according to the Scottish National Dictionary; the same work says that the phrase was later adopted as a slogan to promote G Mackay & Co Ltd’s whisky. The Webster’s Dictionary also quotes Robert Louis Stevenson from 1883 in a letter saying “He’s the real Mackay.”
Read more on the subject at: http://en.wikipedia.org/wiki/The_real_McCoy