I agree Stephen Walt on this:
If you wanted yet more evidence of how unserious the United States is in its conduct of diplomacy, I'd nominate the breathless "will they, won't they?" attention paid to whether U.S. President Barack Obama and Iranian President Hasan Rouhani will actually meet during the U.N. General Assembly meeting. If they do meet, will they shake hands? Will it be an impromptu sidebar or a sit-down conversation? What color tie will Obama be wearing? Will they drink coffee or tea? Boxers or briefs?
For all I know, these and other truly vital questions will have been resolved by the time this gets posted. My main point is that Americans attach too much significance to these sorts of meetings -- mostly because we are too fond of not talking to countries we dislike -- and this reticence cripples our diplomacy. Refusing to talk to people or countries with whom we differ is really just a childish form of spite and one the United States indulges in mostly because we can get away with it. But it also makes it more difficult to resolve differences in ways that would advance U.S. interests. In short, it's dumb.
So boxers or briefs? I don't know but they will inhale.