There are jokes about the air-headed-ness of people with a certain hair color. But I can’t remember what it is. Or what they are. Now I’m all confused.
Subtle as a wet tongue in the ear!!! I nearly literally ROFL’d at that one. Thank you!
"He is a tube light " is popular in India.
“Depriving a village somewhere of an idiot” is a favourite of mine, but it’s generally reserved for people who are actively stupid as opposed to people who are, well, a slice short of a loaf. 
“Slack jawed, mouth breathing, fifty per center.”
He / she is a couple of stands off bottom.
A stand is a length of drill pipe, being off bottom is not having the drill bit in contact with rock. So it is someone who is not entirely there.
Someone who is two stands off bottom but drilling ahead, would be someone who is engaged in an activity in the deluded belief that they are actually accomplishing something useful, but because of their general cluelessness are achieving nothing.
Yeah, I got that in an email, a Southernism: state awful fact, follow with “bless his/her heart.” As in, “She can’t seem to keep a man, bless her heart!” If it’s really lame, add “poor” and pronounce it “pore.” As in, “He can’t seem to stay out of jail, bless his poor heart.”
Eighteen years I have been living in the south and I never knew that phrase was code for moron. I guess that explains why I have been on the receiving end of that comment so many times! :smack:
From a friend:
“That guy is dumb from his ass on up and dumb from his ass on down.” (Es tonto de medio culo párriba y de medio culo pábajo)
Substitute navel in polite company.
Another one:
“The only eye he’s got open is the one in his ass.” (El único ojo que tiene abierto es el del culo)
Most of mine have already been taken. But…
“That boy’s about, I say that boy’s about as sharp as a pound of wet liver!” - Foghorn Leghorne
She’s got a room-temperature IQ
He’s stoopid with two o’s
“Wouldn’t know chickenshit from chicken salad” - LBJ
Fell out of the stupid tree and hit every branch on the way down
He couldn’t organize a two-car motorcade
Mr. President
You could also add:
“He couldn’t organise a piss-up in a brewery” or “He couldn’t find a Chinese restaurant in Shanghai” for someone who is spectacularly clueless or disorganised…
Perhaps off-topic, but I’ve never understood “mouth breather” as a substitute for “idiot.” What the heck do stuffed-up sinuses have to do with stupidity?
Not quite in the spirit, but one of my favorites: He’s as charming as a sack full of assholes, with the good ones picked out.
Think less about folks who need a kleenex as much as the visual of a slack-jawed yee-haw, maybe with a bit of drool coming out one side - kinda like Larry’s brother Darryl - not him; the other one.
Oh, you mean Darryl.
Exactly.
From a co-worker: “Man, she’s so dense, I’m feeling the gravitational pull.”
He musta been behind the door when the brains were handed out.
The porch light’s on but there’s nobody home.
Doesn’t know his ass from his elbow.
And when you really want to bless someone’s heart, you bless his “little ol’ pea-pickin’ heart”.
… and we’re not talkin’ Fahrenheit here.
Sharp as a foam rubber trap.
Mind like a steel trap, rusted shut.
E’s got a brain like a Steel Sieve.