Someone I know told me today that he is “as organised as a very unorganised person.”
In the vein of AngelicGemma’s, I present this gem from a member of my roleplaying group :
"You have about as much loyalty as… I don’t know. What’s something with low loyalty? "
Which is almost a simile.
As Edmund Blackadder once said: “Death and disease stalk our land like two…uh…great…stalking things”
This is from memory from an old Washington Post “Style Invitational” contest: The door had been forced, as forced as the conversation during the ‘contestants chat with Alex Trebek’ portion of “Jeopardy.”
She was as clammy as a french horn player’s right hand.
And one from a drunken Lord Melchitt: “You twist and turn like a… twisty, turny thing.”
I love it. This and the “ice sculpture” one at the top of the thread are my favorites so far 
“I wouldn’t say you’re fat, Garfield, but you have more chins than the Hong Kong phonebook.”
I love Lorne Elliot.
I was just thinking “Madly off in all directions!”
Technically more extended metaphor than simile, but we watched some movie in History class last year… had Gene Wilder and some other guy, took place during the French Revolution… anyway, it started out with an over-dramatic voice-over wondering if the boiling water of revolution would bubble over the pot of France, spill through the burners of 18th century Europe and finally flood the kitchen floor of History Itself.
Clearly, the metaphor was simply taken too far. But it was very funny.
[Jeff Spicoli]
Awesome! Totally, awesome!
[/Jeff Spicoli]
" the pus of his fury"…that’s just…beautiful.
A .sig, from Usenet long ago:
“A simile is like a metaphor.”
I can’t believe I knew this film from this description. It’s Start the Revolution Without Me, with Donald Sutherland and Gene Wilder as identical twins. It’s rather like a mix of Mel Brooks and the Zucker brothers set in revolutionary France.
It truly did have the most painfully extended metaphors ever recorded. Unfortunately Memorable Quotes only has a mild example:
“Duke d’Escargot : I warn you gentlemen, I am not to be trifled with. To pull the tail of a lion is to open the mouth of trouble and reveal the teeth of revenge biting the tongue of deceit”.
And back to the OP, this was another Bulwer-Lytton entry, taken purely from memory:
“Her breasts were like ripe strawberries, except they weren’t covered with little seeds and didn’t have green leaves stuck to the tips”.
Eddie Izzard on practicing the clarinet when he was a child: “It sounded like a cat being scraped backwards over a cat-scraping machine.”
My dick was as hard as a blue quinine bottle.
Like sands through the hourglass, these are the days of our lives. 
I can’t help but add a favorit Bulwer-Lytton submission, though it doesn’t really fit here:
Diarrhea runs in my family.