A performer (singer-songwriter) whom I saw recently mentioned that she holds dual citizenship (child of US parents, born in Quebec). Recently she did a concert tour in Europe, during which her US passport was stolen, so she used her Canadian passport as ID when returning to the US.

She was detained at Customs for several hours by a Homeland Security goon who indignantly informed her that the US "does not recognize dual citizenship" and went on a tirade that included "and if we went to war with Canada, whose side would you be on?"

I don't know what her actual response was, but when she told the story she grinned ruefully and said "hmmm...good question."