This is a perfectly reasonable question asked by personable reasonable people of other perfectly reasonable people. Even expats have a pretty good idea of where they're from. I am not a reasonable person in this regard - therefore, the question "Where are you from?" is one of my greatest pet peeves, because no matter how I answer it, I tend to come across as hiding something (when really, the story is just that complicated).
Friend who shall remain unnamed but let's call her Yolanda: So Nathan, where are you from?
Nathan: Ahmmm Houston, Texas.
Y: Oh! And which high school did you go to in Houston?
N: An international school, actually it was in London.
Y: London, Texas?
N: No - London, England.
Y: England isn't in Texas.
N: Wait, seriously?
Y: But you said you were from Texas?
Y: But you didn't go to high school there.
Y: But you were BORN in Texas.
Y: Not born there AND didn't go to high school there...okay, where WERE you born?
Y: So why don't you just say you're from Minnesota?
N: I haven't lived there since I was a toddler and I remember almost nothing about it.
Y: Okay. Well where have you lived the longest?
N: Texas...I think. Depends on how you slice it.
Y: But you don't live there now.
N: Y-...no, it's complicated.
Y: Well where do you live now?
N: The Hague, Netherlands.
Y: Why on earth are you there?
N: Work assignment.
Y: Oh! What company?
N: Chicago Bridge & Iron
Y: ...I thought you said you worked in The Hague?
Y: But your company is Chicago--
N: No, that's just what they're called. They don't really do much bridges/iron stuff either.
Y: But their headquarters is in Chicago?
N: No, they're headquartered in The Hague.
Y: Oh. So why are you working for a Dutch company?
N: They actually hired me out of Texas - they have a lot of stuff going on there.
Y: How did you end up in Texas again?
N: Probably airplane or car like a normal human being? I don't know.
Y: Well, did you maybe go to school at UT or Texas A&M?
N: No, I went to school in New Jersey.
Y: Of course. But like, people are sort of defined by where they went to high school. So how come you don't say you're from England?
N: Well, I used to say I was from London, but people called me "fake British" because I dropped the accent when coming back to the US, so I just started saying I was from Texas.
Y: So you're really from London?
Y: Would you call London home?
N: Probably not, like I can't recommend any favorite pubs or anything. I love their TV though.
Y: Where are you going to fly home to see your family next?
N: North Carolina.
Y: Oh - so your parents live there now?
N: No, they live in Texas.
Y: Back to Texas...so you'd say you're from Texas.
N: That's my story, and I'm stickin' to it.
Y: Are you like a huge Ted Cruz fan?
N: Not...as such...
Y: But you ain't got no southern drawl neither. But you say you're from Texas. I don't buy it.
N: LOOK I'M FROM MARS OKAY YOU GOT ME NOW TAKE ME TO YOUR LEADER