More often than not, I've seen screaming or very rude demanding actually work in the US. It is very upsetting to see gate agents cave in to rude people, because that encourages these people to be rude the next time. However I have never seen it work in Europe. I actually love to see Americans go off on LH staff at FRA or the AF staff at CDG. They often end up crying and apologizing after being told they have been removed from the flight in question and any other flight that day.