You take an average sentence, and add a plot twist. But in the next post, there's another plot twist- and another in the next- and so on. Example:
Post 1: Johnny woke up on a sunny morning...
Post 2: ...to find he was on Mars!
Post 3: But then he was kidnapped.
And so on. Except, you know, more awesome then that because my examples suck.
I'll start (no durr):

Johnny woke up on a sunny morning...

but the 'sun' was just a bright light coming from..


(something like that? :x)

...coming from the neurosis in his brain...

... which actually was the side-effect of a government chip implant

...which had been placed on his trip to the future...

...in order to erase that Orwellian future.

But he didn't remember a thing...

...so he brushed his last remaining tooth...

...not realizing his toothbrush was a laser...

That turned everything into cavities and...

his Orang Tabby cat exploded...

...because it was a weapon sent by...

Nazi Germany!

Meanwhile, someone knocked on his door...

but he realized it was his back door, no one used the back door...

except the hells angels who delivered his weekly paper and...

Arnold Schwarzenegger who came in for some pizza.

and said, "I'm back!"

Arnold, irnoically, is there to...

return the tooth he borrowed...

cause Johnny is actually the tooth fairy.

who dresses up in a tutu made of old vinyl records...

and those records actually contain the audio of every United States conspiracy and secret...

many of which were used as scripts for TV greats such as Stargate, the X-Files, and Terminator.

(haha nice:))so Johnny and Arnold go to a bar in the rough side of town

and Gary Busey suddenly runs in with a gun claiming he'll kill everyone

But Johnny's girlfriend, Minnie the Moocher, flings herself in the way

Gary Busey laughs and shoots her in the leg

But it turns out the bullet is deflected

Arnold's dead body falls to the ground.

Jesus arrives frantic, cause like Chuck Norris, the death of Arnold would mean the Beginning of the apocalypse, so jesus...

Throws a wild wine tasting party

With hopes to find a new Arnold to replace the old one.

But then the lights go out!

Turns out, Arnold was the source of all the worlds electricity.

...because of his being the son of Thor, God of Thunder, who burst through the window!

...and demands to know why Jesus didn't invite him for wine tasting

But Thor realizes he's broken the wrong window and is now in Alchoholics Anymonous.

But Thor realizes he's broken the wrong window and is now in Alchoholics Anymonous.

But then Alchoholics Anonymous turns out to be a vampire rehab called Bloodlust Anonymous!

And as it turns out, Bloodlust Anonymous is headed by none other than the Olsen Twins.

And as it turns out, Bloodlust Anonymous is headed by none other than the Olsen Twins.

Both of whom have donned an evil hand puppet each which appear to have lives of their own
but then...

Both of whom have donned an evil hand puppet each which appear to have lives of their own
but then...

Danny Bonaduce swings in through the window on a borrowed Tarzan vine and attempts to lecture the girls - via the hand puppets -into giving up their evil ways, using himself as an example.

Only one of the puppets didn't fit.

Then the puppets exploded.....yeah

But the fragments turned into evil bloodsucking giant leeches and leaped on all those present while a time-warp caused by the explosion tipped them all into a medieval castle in the Black Forest.

Then a Black Knight riding on a fire-breathing donkey rides up and says "Aye!"

"Aye m'laddie i am to take ye away to the castle on Jupiter where the nijas love to eat strawberry ice cream!"

But he doesn't & takes you to utah instead. There you are surronded by british cowboys who love the hokey pokey.

Then you try to escape the hokey-pokey dancing british cowboys through a window.

But the window is a passage to a TARDIS, piloted by sentient otters!

The otters drop you off on the planet of the apes.

The otters transform into decepticons which battle the apes for dominance of the world

And the decepticons are all like "IMA CHARGIN MAH LAYZAH!!!"

But the apes stand firm. "Cash only!" they growl.

And then Foxy Mahallen, your ex-lover, appears from the shadows!

They she fires her LAYZAHS!!

Dejected, the LAYZAHS sign up for unemployment benefits.

They she fires her LAYZAHS!!

The Golden Yak descends from the heavens, sheilding her from the LAYZAHS.

Then a spartan kicks her down the pit of death

The LAYZAHS, denied their unemployment benefits, try stealing from the Spartans, not realizing that all of Sparta is flat broke.

So instead they try to steal from Mr Gordon Brown, who happily has far too much money for his own good the greedy retch.

But when they steal it, the money grows mouths and begins to attack everyone present.

So they take a giant sledghammer and chainsaw to the money, then realise too late they have hacked up their fortune! :O

Then then Leatherface shows up to take his chainsaw and sledghammer back

Because he needs them to break through the force field that has just been put around Earth, threatening to choke all its inhabitants!

Because if everyone's head explodes from choking somehow he'll have no more faces to steal and where and so starts running around like the madman he is

But he is cured from his madness, and comes across a depressed and very beautiful girl, because he has traveled far in his running aound recklessly.

But the girl turns out to be a well disguised tranny and solicites you for.... dirty things.

He doesn't care though, because he likes dirty things.

Even though he has a severe case of OCD, and has to clean everything twice, every day.

But cleaning everything only makes everything brighter and reflects the light right into his eyes, making him blind.

Fortunately the blinding light is focused to the point of singeing the feathers off the Gryphon that came to kill him, sending the Gryphon on a death spiral to the ground.

But a trampoline catched the griffin. And the man is still blind.

ROFL its caught :-P

But the man is protected by angels, they were called by the bright glittering lights of his shining.