I've often heard this line in various forms, most recently in a WallStreet Journal article that's generally sympathetic to gun owners: "Growing up in Seattle, I knew nobody who owned a gun."
The striking thing is that this statement is almost certainly false: I strongly suspect that anyone growing up even in a very insular corner of Seattle did know people who owned guns. He just didn't know that he knew them, because they weren't telling, and one of the reasons they weren't telling was precisely the casual assumption that of course no-one in their circle would ever do such a thing.
This is a common phenomenon (labeled "preference falsification" by Timur Kuran when it has to do with attitudes rather than behavior). If a particular practice is socially frowned on by some, then the substantial minority -- or sometimes even a majority -- that engages in it may hide its behavior, leading everyone to dramatically underestimate the prevalence of the practice. So you can have 20% of the population owning guns (much less than the national average, but perhaps it was the average in the author's Seattle circle), but this 20% actual prevalence would look like a 2% prevalence or even a zero prevalence.
The quote reminds me of Justice Powell's famous line "I don't believe I've ever met a homosexual," said at the time Justice Powell was considering his vote in the Bowers v. Hardwick (1986) gay sex case. (See John C. Jeffries, Jr.'s biography.) Powell had by then had several gay clerks, and apparently said the statement to a clerk who was himself in fact gay. Powell's belief that he'd never met a homosexual was much like some people's belief that they didn't know anyone who owned a gun.
This also helps show the wisdom of many gay rights activists' view that coming out to friends and family is itself a potent political action. It's much harder to demonize that which your friends happily do than that which no-one you know would ever dream of doing. (Still possible to criticize it, of course, but harder to demonize it.) Gun owners in relatively non-gun-owning circles -- especially the well-liked and good-looking gun owners -- should do the same.
The article's bottom line, by the way, is that surveys report that gun owners aren't particularly likely to be "bitter," but are actually a little more likely to be happy than non-gun-owners; as I said, this is not an anti-gun article. Moreover, the author might even, on reflection, realize the error of his statement, especially given his consciousness of "how little some Americans know about their neighbors"; he might have actually meant to say "I knew nobody whom I knew to have owned a gun." But the way he put it still strikes me as telling.