The "Real McCoy"

During the prohibition era, many people became ill or even were killed due to poisonous home-made alcoholic mixtures known as "hooch" or "shine" (short for moonshine). A rumrunner/bootlegger named McCoy had a good three year run using a ship to import genuine alcohol to the united states, and became famous for carrying only the highest quality liquors. His cargo became referred to as the "Real McCoy", and the term became a common way of inquireing as to the authenticity of liquor products, and is commonly used today to inquire as to the authenticity of just about anything. McCoy was intercepted and arrested by the U.S. Coast Guard in 1923.

Real deal.
Oilers on early trains had to be oiled to stop friction on the drive wheels. Oilers always failed... except the McCoy brand and they became known as the best and 'the real McCoy'

the genuine article
a true original

The genuine article.

1. The real deal.
2. A brand name for chips in Britain/Europe.

In the legend of the bitter feud between the Hatfields and McCoys, a bloodline offspring of the McCoy's was the real McCoy. A child born from parents consisting of one Hatfield and one McCoy was not a real McCoy.

Therefore anything that is not genuine is not the real McCoy.

Someone who stays online but refuses to read or answer your messages because they think they're cool.