I've observed situations like this occurring to a friend of mine (let's call him X):
Stranger: Where are you from?
X: [insert southeast asian country here]
Stranger: Are you sure?
...
On very rare occasions, people are more direct/rude, and they'll ask this instead:
Stranger: Are you sure? Aren't you from China/Japan/Korea?
The most comical situation I've witnessed:
Stranger: Where are you from?
X: [insert southeast asian country here]
...
Stranger: [insert question about China/Japan/Korea]
X: I don't know. I'm from [insert southeast asian country here].
...
Stranger: [insert question about China/Japan/Korea]
X: I'm not from China/Japan/Korea.
Stranger: Oh. Then where are you from?
X is ethnically Chinese. His family left China sometime in the 1700s-1800s, and they settled in different parts of Southeast Asia, and later, in different parts of the world.
I'm wondering if there are appropriate responses to such situations. How can one deal with people who do not believe where one claims to be from? Do you repeat yourself? Do you repeat yourself more than twice? Do you give a better/longer default answer when others ask where you're from?
(Note: To X, there is no problem. He seems to think that these situations are normal, but I'm asking out of curiosity because "home" is central to the identities of most people, and it must be rather confusing when others don't believe that your home is where you claim it is).
EDIT: X is really from Southeast Asia. He lived in the region for most of his life, and so did his parents, grandparents, great grandparents, great great grandparents, etc. He now lives in Canada on a long-term, but temporary basis (i.e. he has definite plans to leave). The situations shown above come from conversations in Canada, and in conversations in the U.S. when we were traveling together.