Where I'm from, 1wabbit1 is correct in that screwed the pooch means to fail utterly.

To express "not doing much of anything" in terms of canine coitus, we use dickin' the dog.

I begin to think that with a little creativity we could come up with ways to express nearly any situation in such terms.

And with that thought I'm sent spiraling off-topic.

So, to express "I'm feeling left out/abandoned," I hereby submit: Lovin' the Labrador.
Man, all my friends went to a concert together and I'm left lovin' the labrador.

To express being on top of the world/confident/full of one's self: Gag a Greyhound.
I am such a stud today I could gag a greyhound!

"Well spank my ass and call me Charlie!" (An utter of surprise, I hope.)

Sawbuck- Ten dollar bill.  Wish we still said this; it's catchy.

Worth a Plugged Nickel- As in the phrase, "Get out of town by sundown or your life won't be worth a plugged nickel."  I've also heard "Plugged Peso".

There are a lot of good euphemisms for hangings:

The Steps and the String
The Gibbet
Long Walk and a Short Drop
String up/Strung up - Used as verb, "To String Up"

Also lots of good ones for dying:

Bought the farm or, often, just "Bought it"
Cut Down
Went on to His/Her Reward


Finally, there's "Shanghai".  There used to be an area of San Francisco along the docks with a lot of seedy bars (commonly known as the Barbary Coast).  It was not uncommon for men, especially gold-rush era miners, to wander into these bars with a lot of money and get drunk.  It was also not uncommon for such men to wake up on a ship bound for the Far East, their money gone, forced to work as deckhands.  From this, we get the term "Shanghai", to force into something.  "I just got Shanghaied into helping my friend move."

We should probably listen to Keech.  He's older than writing.

There's a few here and there that I still people around my town say

Fair to Middlin(Midland?) - as in " Hey how are you?" "Oh fair to middlin" doing alright, not too great, not too bad

Cunt hair - Something thats really close ie "Its only off about a cunt hair"

6 of one, half dozen of another - Basically means the same thing or pretty damn close

Homely - ugly

Queer as a three dollar bill

I know there's more, some probably better than those, but can't think of any others off the top of my head.

Mealy-mouthed morphidite was one of my old time favorites....my maw Maw used it on a plethora of undeserving bystanders...Don't ask me what a morphidite is my Maw Maw swore it meant something..

Well she is a Cajun coon ass that speaks Cajun french originally so I guess that's how she interpreted it haha..

I will die a happy man if I can find a proper occasion to say that to someone. 

Oh really, I hear it at the end of sentences (sometimes as"Bob's your aunty"), when someone's planning something out. Meaning "everything'll be okay", akin to "she'll be apples".

I can never consciously bring myself to call All Hallows Eve 'Halloween'.

Its ingrained from my childhood and I never thought anything of it until my girlfriend started making fun of me for it last month.

I also say 'lovely' instead of 'that would be great' etc...All the time. Its worrying.