In 1909, Twain joked that the next time Halley's Comet passed close to Earth, he would "go out" with it. He didn't mean romantically: The comet had last been visible from Earth in the year Twain was born, 1835, so he claimed it would be the "greatest disappointment of my life" if it didn't also pass at the time of his death. According to Twain, God must have said, "Now here are these two unaccountable freaks; they came in together, they must go out together."
Edward Emerson Barnard/Yerkes Observatory
"Preferably in one world-ending fireball."
True, Twain was advanced in years when he said that, had some heart troubles, and was depressed about losing some family members and close friends, but he was by no means on his deathbed or expecting to go to the big steamboat in the sky anytime soon. He was writing and active in his anti-imperialism league all the way to the end.
As you might know, Halley's Comet visits us once every 76 years and is only visible from Earth for a couple of months at a time. This means that at the moment of Twain's humorous prediction, the comet was due again in the following year; and what do you know, it showed up on April 20, 1910. The next day, Twain died of a heart attack.
Clearly, just dying in the same year the comet passed or at any time during its two-month window wasn't impressive enough for Twain -- he had to do it mere hours after the thing first showed up, didn't he?