The shit that can hit a fan is not true shit.
What is the sound of shit hitting a fan?
If a bear’s shit hits a fan in the forest does the Pope hear it?
Only if it’s Zombie shit.
Shaggy dog stories and Feghoots are entirely separate classes of jokes. The classic shaggy dog story is very long and often arrives at an anticlimactic conclusion, the point being to frustrate the listener after the interminable build-up leads one to expect a gigantic ringing note of an ending. Feghoots are always very short and always lead to a specific example of a sentence-long pun.
Your cite has it totally wrong. TVTropes has it correct. You’ll have to believe me when I say that I wrote my post first before linking there, but our definitions are essentially identical.
The ship hit the sand.
The ship hit the span.
Anybody else got any clean euphemisms for the OP’s phrase? Besides Zelazny?
The joke in response #7 spread through my grade school in 1946-48 or so.
To paraphase The Big Bang Theory:
When the waste material contacts the spinning turbine.
http://the-big-bang-theory.com/quotes/episode/222/The-Classified-Materials-Turbulence/
If you had been there you might understand,
I was a very bad chef in NY, NY twenty years ago horrible job, the tales I could tell you!
Anyway we had an explosive Sewer explosion in the Kitchen, literally everything covered with sh1t and the Rats who were also blown out of the drains, (sorry no Alligators, urban myth), meal was served to a certain RG Mayor of NY.
Hey Ho. Happy 2012
Ever have a fan outside on the deck or in the yard?
Bird flies by and …
nuff said. 
It can happen.
It has been noted that the zero-g toilet on the space shuttle contains a “rotary mechanical separator” to separate the solids from the liquids. It has been remarked that, in this design, the shit is SUPPOSED to hit the fan.
with all due rspect to TVTropes, I grew up calling contrived stories that ended in a bad pun a shaggy dog story.and apparently so did the people in this thread
The OP of that thread said:
If he or she has to make an issue of a pun ending, then all shaggy dog stories don’t end that way. But they are all long. I think you need a better cite.
Of course, if everybody uses shaggy dog story in that way, then it will come to take on that meaning. That’s the way language works. But I don’t think the transition has happened yet.
Not to put too fine a point on it, but there is a period of suspense between the time when the shit is directed toward the fan and impact. This mental stress during this period, in which you can do nothing but duck, is arguably as bad as the fallout.
There is: “The shit’s gonna hit the fan when mom finds out what you done!”
And then there is: “The shit really hit the fan when mom got home last night.”
Both tenses of the metaphor have markedly different uses.
The high humor point of a hilarious low brow movie. That and “I’ll check the radar range.”
U.S. Military, origins in WWII.
Well, okay, not a biggie thing to argue about (I think). But your classification doesn’t seem to include the very long (like shaggy dog) story with the sentence-long pun combination, which is what I considered to be a “shaggy dog” story. Whatever my cite might have wrong about the terminology, it’s still a good compendium of them.
ETA: Here is a version of the story that I thought gives “Shaggy dog” stories the name – In some tellings, the dog is actually a shaggy dog, like a sheep-dog maybe. Aha! Jokes > Funny Puns > Helping out the knight