Surprise: “Well Jesus McF*ck!”
The variation I’d heard on the ‘busy’ one was “Busier than a one-armed bandit.”
“You lie like a cheap rug.”
“Dull as dirt.”
Lazier than a bump on a pickle.
And a variation…Too pooped to poop.
On attractiveness:
‘But would you run barefoot through seven fields of broken glass just to slide in her shite?’
‘I wouldn’t touch her with yours’
‘I’d say she has a Mary like a wellytop.’
‘A face like a bulldog licking piss off a nettle.’ (thanks Billy Connolly)
On exteme hunger:
‘I’d eat shite of a scabby leg.’
‘I’d eat a nun’s fanny* through a convent gate.’
‘I’d eat a farmer’s arse through a hedge.’
On nipple erections (I know too many phrase to do with nipple erections):
‘…like hatpegs.’
‘… like fighter pilots thumb’s.’
‘… like monkey’s fingers.’
On the reputation of ladies:
‘If you kicked her in the arse a bag of mickeys** would fall out.’
On finding that something is only superficially attractive:
‘Like buttered shite.’
On ineptitude:
‘Like a one-legged man in an arse-kickingcontest.’
‘Couldn’t find his arse with both hands and a map’
On meanness:
‘He could peel an orange in his pocket with boxing gloves on.’
And I don’t know what this refers to, but it cracks me up: ‘Ah, but where would you be with bell on your bike and your knickers wringing?’
- Fanny means a different thing over here than in the US.
** Mickey: Irish (Dublin?) slang for penis.
I like “busier than a two peckered goat”, “you talk like a man with a paper ass”, referring to someone who doesn’t know what thay’re talking about, “he snuck up on me like a pair of cheap underwear” and “when God was handing out brains, he thought He said Trains and said, ‘no thanks, the whistles hurt my ears.’” My sister’s father-in-law “Fast Eddy” had literally over two hundred sayings that we documented and called “Eddyisms”. Unfortunately, we lost the list over 25 years ago. I’m sure my sister’s husband can recall more.
My own favourite on being unlucky in love:
“If I fell into a barrell of tits I’d come out sucking my thumb”
How true 
micilin: thanks for the international perspective. I’d say “I wouldn’t touch her with yours” is a cleaned-up version of “I wouldn’t f*** her with a stolen dick.”
And over here, fanny = cleaner, more acceptable version of ass (or arse, as you would say.)
Mary?? wellytop??
on sanity:
He’s about two knights short of a crusade.
He’s about two fries short of a Happy Meal.
on intelligence:
He ain’t got half the brains of a bag of ferrets.
Boy, you’re about as dumb as a box of hair…
On wishful thinking:
Yeah, and if a frog had wings, it wouldn’t bump its ass a-hoppin’.
Said of an ugly woman: “She looks like her mother fed her with a slingshot.”
Of a pretty woman “She has a body that’d make Jesus Christ climb down off the cross.”
In the military, bogus acronyms constitute a form of colloqualism: eg. SNAFU, BOHICA, and my favorite: “Proceed to carry out E-tripple-S (off-duty, free to eat, sleep, smoke and shit)”
Couple of my favorites (these are actually quotes from Waylon Jennings as the Narrator on Dukes of Hazzard):
They took off faster than bad news travels.
This thing’s got more turns than a bucket o’ worms.
Havin’ more trouble than two stray heifers in a pasture full of bulls.
He’s got more wrinkles than a bucket o’ prunes.
Trapped like two foxes in a hen house with a sack fulla eggs.
Smugger than a hog knee-deep in slop.
Madder than an old wet hen.
Stickin’ out like a bourbon bottle at a country revival.
from NinetyWt: I wouldn’t fck her with YOUR dck ('scuse me)
My guy friends use a modified version of this that goes:
“I wouldn’t f*ck her with [other person’s name]'s and [secondary person’s name] pushing.” Almost always in reference to a person’s lack of attractiveness or ability in bed.
Ooops. Correction: “I wouldn’t fck her with [other person’s name]'s dck and [secondary person’s name] pushing.”
On being scared, “You couldn’t have pulled a pin out of my a$$
with a tractor”
Someone trying to do something they’re not capable of, “Don’t
monkey with the band if you can’t toot a horn”.
Saw a bunch already which made me chuckle in memory, being the transplanted child of Southerners that I am, but here goes.
On an individual blessed with a sizeable nose:
“S/he could gut a punkin through a rail fence.”
On roadkill, someone passed out from drink or other substances, or someone knocked out from a blow:
“Knocked him/her flatter than a flitter*.”
On someone who is stingy with their money:
“Tighter’n a hen’s flitter.”
On a particularly close friendship or business acquaintance (generally of a shady sort):
“They’re [stuck together] tighter’n pig turds in July.”
On someone who is creating a scene or highly upset:
“S/he’s pitchin’ (pitched) a hissie fit.”
On someone known for less than legal dealings:
“S/he’s as crooked as a dog’s hind leg.”
On someone who’s worthless:
“Ain’t fit to carry guts to a bear.”
And my personal favorite (pardon the phonetic spelling; for the life of me, I have NO idea what this word really is, except possibly a derivation of ‘carrion’):
On people or a family who are dirty/low-class/trashy:
“They’re just kearney.” (pron. kee-YAR-nee)
Gotta love colorful language.
- Outer female genitalia.
My dad was a native Texan (or Texican, as my 5yo nephew calls 'em), and he had a seemingly endless supply of these. Some of my favorites:
He couldn’t find his ass with both hands and a flashlight.
That’s enough to piss off the pope.
That’s enough to make the pope kick out a stained glass window. (Usually used when he saw an extremely attractive woman.)
That’s good enough to make you want to slap your granny and dare her to get up.
Slightly OT, but he also taught me the “sleep tight, don’t let the bedbugs bite” thing when I was very young. He added his own ending, though: “If they do, crack 'em in two and eat 'em like the monkeys do.” I was in college before I realized he made that part up.
Scarred for life. It’s enough to piss off the pope. 
Couldn’t pour water out of a boot with the instructions written on the heel
Proof that evolution can go in reverse
As smart as bait
An intellect rivaled only by garden tools
An experiment in artificial stupidity
“I’m slicker than a mashed potato sandwich” some kid said this during Latin today. I about laughed myself silly.
And I’m fond of saying “He’s not the shiniest crayon in the picnic basket,” because I like the mixing of metaphors.
An insult my friends and I made up and actually use: tampon licker.