"You Guys!" was an insult. But this expression was transformed into a term of endearment, in America, by the working class. Because that is what the working class do.
Gunpowder Plot
You are probably familiar with the Gunpowder Plot, in which Guy Fawkes, attempted to blow up Parliament on 5 November 1605.
And thus, because Guy Fawkes was reviled for his crime, the expression "You Guys" emerged as an insult.
Norman Conquest
But how did an Englishman come by the names "Guy", and "Fawkes"? According to Wikipedia, Fawkes is a name of Norman-French origin.
Well now. It just so happens that the Normans invaded and conquered England in 1066, an event from which the history of English Nobility ever since can be traced.
Guy of Nantes
And yet more than a half century before the Normans even settled in Normandy, which they would not do until the middle of the 9th Century, (from where they would later sail across the English Channel and conquer England), Guy of Nantes was Count of Nantes, as of 778, which was of course the late 8th Century, the County of Nantes being located next door to what was not yet Normandy nor inhabited by Normans, and Guy (of the Guideschi Family), not being Norman but Frankish of descent.
Well, that was awkward.
Breton Peninsula Geography
So who was Guy, who were the Guideschi, and why were they occupying a small principality in between what are today Normandy and Brittany in the NorthWest corner of France?
If you will recall that Charlemagne became King of the Franks in 768, but he was never able to conquer the Breton Peninsula, because the terrain was too rough. Thus he appointed Guy's father Roland as Count of Nantes, intending for the County of Nantes to be a buffer zone of containment protecting the Carolingian Empire from the inhabitants of the Breton Peninsula, (who could not be conquered on account of the rough terrain).
Excile to Italy
Anyway, one thing led to another. Guy's son Lambert had a falling-out with Charlemagne's son Louis the Pious, which resulted in the Guideschi Family being exciled to Italy.
And then in 834 Lambert was given the Duchy of Spoleto, even though he was exciled, and the Guideschis firmly ensconsed themselves in the chaos and intrigue of what at that time passed for statecraft in Italy.
Conclusion
In conclusion I really have no idea where I was going with all this, but thanks for reading all the way to the end, you guys!
Here's a podcast about the Guideshi.