I for one have always been fond of
“Not the sharpest cookie in the shed”
or at the amusement park we got alot of mileage out of one phrase after an election day. a really trashy scraggly looking guy, poster child for the term white trash came strolling in, bearing an “I VOTED!” sticker upon his shirt.
From there on out, less than quality folks we referenced as “Theres a registered voter for ya”
Ive always liked
“You have the mental agility of a broken soap dish.”
Dumb as a stump
Two sandwiches short of a picnic.
As thick as two short planks sawn in half and nailed sideways.
As sharp as a billiard ball with all the edges filed off.
The elevator doesn’t go all the way to the top floor.
A guy I knew in college referred to another classmate by saying he “doesn’t have the brains God gave a fly’s scrotum”.
I am so using this at the first opportunity.
Usually I say “dumber than a box of rocks.”
sometimes I say, he so dumb he has to take off his shoes to count to 11.
At times I have said, he is so dumb that he got arrested for indecent exposure while playing blackjack.
A college friend taught me “He’s stoopid with two 'o’s,” which I’ve always loved.
Stoopid!
I use some form of, “If you had the sense god gave a …” a lot. Drop in “hamster,” “cockroach,” “onion,” “boiled egg,” or whatever, to taste.
[QUOTE=Hostile Dialect;10781503"He just kept turning it over like a monkey trying to fuck a football."*[/QUOTE]
I’ve always heard and said, “It was like five monkeys trying to fuck a football.”
At work, when there’s a mess, someone will usually say something like, “The other four monkeys are still working on it.”
“He’s strong as an ox…
… and almost as smart.”
S^G
Doesn’t have the brains God gave a head of lettuce.
Couldn’t pour piss out of a boot if the directions were written on the heel.
Needs to be hit with a clue-by-four.
LBJ was quoted saying that about some Congressional foe. He also said someone “didn’t know shit from Shinola” (a shoe polish of the day), and suggested that then-Congressman Gerald Ford had played college football without a helmet on (i.e. was brain damaged).
“One brick short of a full load”
“The doctor didn’t slap him hard enough!”
“Your idea is dumber than snake mittens!”
Can’t hit the urinal on the first squirt. (Steven King, from The Shining)
Can’t find his ass with both hands and a map.
Couldn’t figure out which end of the hammer to shove up his ass.
Too dumb to fuck a sloth, but dumb enough to try.
Wasn’t fit to shovel shit from one place to another.
A member of the ‘Green Side Up’ brigade. (Said of landscapers who can’t be trusted to lay sod without supervision.)
From my southern youth:
“He’s so damn stupid he doesn’t know his ass from a hole in the ground”
I got a chance to use Hostile Dialect’s one already!
We have a dumbass neighbor whose tricked-out Chevy POS has been showing signs of dying for several months now. Last night, it wouldn’t start at all. He kept turning the key in the ignition, and despite the fact that it chugged but wouldn’t catch, did it over and over and over again. Then he’d get out and, for some reason, repeatedly slap the exhaust pipe really hard. Back to turning the key. This went on for a couple of hours.
Then, with perfect timing, I delivered HD’s line: “He keeps turning it over like a monkey trying to fuck a football!” and got a tremendous laugh out of my husband. Of course I took credit for inventing it.
Thanks, Hostile Dialect.
I’m just glad it got put to good use! Just pay me my royalties and we’ll be good. 
Hostile Dialect,
Hostile Dialect, Narcissist
“His family tree doesn’t branch”