In terms of authors, “Happy birthday!” In terms of their stories, “Happy doomsday!” Here’s an apocalyptic triptych (though only one features full frontal nullity).
John Barnes (1957-02-28)
“My Advice to the Civilized” (IAsfm, April 1990)
In the near future, a few years after civilization has collapsed, a former historian and current sergeant in a Company gets ready for battle with an invading, sadistic, murderous, barbarian Horde and writes a letter to the future. Through this letter, we learn something of what happened, what is happening, and what will happen while we mostly get a half-dozen bits of advice which the historian expands upon in a reflective and heartfelt way, thinking heavily upon the loves of his life.
The relatively minor flaw in this story, for me, is its present-tense narration which is rarely a good idea and especially not here. If I’ve been writing a letter, get interrupted, and have returned to the letter afterward, I don’t write “I sit down to write more.” The far more important strengths are the strange believability of a strangely inexplicable collapse of civilization, how the civilized grow more barbaric in response to barbarism, the complex attitude toward both civilization and barbarism (with civilization clearly the favorite), and an interesting effect from its incomplete ending which can be read as completely tragic or somewhat hopeful depending on where you stop in your own continuation of the story. This is also (as it would often be) a timely story.
Edgar Pangborn (1909-02-25/1976-02-01)
“The Red Hills of Summer” (F&SF, September 1959)
After humanity has wrecked Earth, three hundred humans have fled in a spaceship (possibly one of a few) and has found a new world to attempt to colonize. Four people are chosen to go down and test its suitability before the rest may join them. A quiet religious woman, a high-strung and odd political theorist, a fairly ordinary guy (our narrator) and his wife descend to the planet’s surface. What follows is quite a bit of action as the group establishes a landing site, deals with the native life (none sentient but some quite dangerous), and with each other, mixed with some contemplation on why Earth went wrong and whether this world will, too.
There is often a divide between the usually sharp, pragmatic, literal, but sometimes thin “hard SF” and the sometimes deep, philosophical, metaphorical but usually fuzzy “literary SF” that I wish were bridged more often and better. I don’t recall having read Pangborn before (though I’ve certainly heard of him because Gardner Dozois was such a fan ) and I’d assumed he was pretty far into the literary territory but this story, at least, is a very nice blend. I do think the story has a couple of flaws (it obtains some of its conflict by having an implausibly poorly planned and executed mission and there is a moment of great tension for the characters at the end which depends on what immediately feels like overreaction so that the tension feels forced for the reader) and I wish “literary SF” didn’t so often depend on ruined Earths but this was generally a very good story which a variety of readers are likely to appreciate.
Theodore Sturgeon (1918-02-26/1985-05-08)
“The Hurkle Is a Happy Beast” (F&SF, October 1949)
On the planet Lihrt, a gwik creates a disturbance which causes a lab to be deserted which allows a young hurkle (a gwik pet) to unwittingly modify a gizmo and then accidentally fall into it, which results in the hurkle materializing on Earth. It disturbs a classroom, causing a very level-headed (but inexpert) teacher to try to deal with it, which results in a great change for both humanity and the hurkle.
This is told in an almost fairy-tale way which usually annoys me. In this case, it doesn’t, because this is a very funny (though also dark) story in which the “mimsy were the borogroves” methodology is put to great (and sometimes risque) use as we’re told how life went on after the disturbance at Lihrt and the gwik still “fardled, funted and fupped.” Sturgeon was one of the best and could do all sorts of stories from hard SF to fantasy to mainstream and from comedy to tragedy to horror. This particular one may not be his most momentous, but it’s entertaining.
 And I’ve got a couple of Pangborn’s books in the Pile, mostly on the strength of that.