I don't know exactly when 9/11 became a household word, although the New York Times, apparently, first ran it in print in an editorial the day after the attacks. Regardless, it has become so widespread — and fits so easily into phrases like "after 9/11" and "in a post-9/11 world" — that it is hard to remember a time when we didn't evoke it constantly.
It seems a sure bet that we will continue to evoke it for years to come; consider how terms like Waterloo and Custer's Last Stand become part of our vocabulary long after many people can even remember what they mean. Perhaps 9/11, like those events, will sink into the lexicon as an all-purpose term for disaster.
If Cameroon, say, suffers a massive earthquake in 200 years, will the pundits forget about terrorist connotations and simply label the event "Cameroon's 9/11"?
Of course when catastrophes grow distant enough, they become fair game in other ways. Mel Brooks made one of the most successful comedies in history by ridiculing the Third Reich; "The Simpsons" has knocked off countless jokes about Vietnam; Ben Stiller drew few if any protests by comically restaging the Lincoln and Kennedy assassinations in "Zoolander."
Carol Burnett was famously quoted as saying, "Comedy is tragedy plus time." In the few years after 2001, I seldom heard a 9/11 joke — Gilbert Gottfried drew a hostile response by telling one at the Friars Club weeks after the attack — but when a character on "The Office" recently apologized for misbehavior by saying, "I think I never really processed 9/11," it sounded surprisingly less jarring than it might have half a decade earlier.