It's never enough to say you're from London, people want to know exactly where you're from. They see it as more of a test of their own geographical knowledge. You say "I'm from London" people go [high pitched excited voice] "Where abouts, where abouts, where abouts, where abouts exactly, where abouts?" "Uh... North London." If they know it they get more excited. [more excited voice] "Where abouts, where abouts, where abouts?" "Muswell Hill" [even more excited voice] "Where abouts? Where abouts?!" "Do you know Sainsbury's?" "Yeeeeeeessssssssss!"