I seem to be unusual in America, but I object to those who think we should address foreigners by their titles or deferential forms of address.
For instance, I don't think a duke should be addressed by an American, in America, as "Your Grace."
I'm an American, and I don't recognize titles of nobility.
If I ever go to UK, in politeness I will attempt, no doubt ineptly, to follow the local customs in such matters. But then I expect foreigners, in politeness, to accept American customs when they come here.
I make exceptions for foreign heads of state, such as the Queen, when visiting America. But that's a nod to the sovereignty of her nation, not to her as a person.
I get seriously torked when commenters on the NRO website routinely refer to Conrad Black as Lord Black.
I don’t favor Americans bowing to foreign heads of state — at all! But certain dress protocol respectful of the office, such as avoiding showing a lot of nude skin, as well as respecting a head-of-state’s personal preferences about whether a foreign official or his wife can lumber up and hug an 86-yearr-old woman are a matter of diplomatic courtesy that should be observed.