I've always wondered that for the Men of Cornwall...
They're Cornish.
I refer to myself as English because I am not Scottish, Irish or Welsh, so I can't say I'm British. But everyone else not from England calls me British, so what the hells ^^
mmm.... well 'officially' we are British. But as you say I feel no affiliation with the other member states of the U.K.. Plus, as with most things in life, I go by football so I'm definently Engish there. Might change if the GB football team do well at the Olympics :P
You have one nationality, as stated in your passport/identification papers. You can have multiple ancestry, but if your passport states you're American, you are American.
if you mean me, it's not racist at all. someone's nationality doesn't tell nearly the story that someone's ethnicity does and therefore isn't as entertaining. by entertaining i do not mean point and laugh entertaining. by entertaining i mean that it tells, albeit with very little detail, the story of one's family's travels. in that short telling you can find common ground and thus more entertainment. none of which is racist at all.