"...I think you forgot to pay your brain bill."
"The lights are on but nobody's home" seems to be in the same vein.
Blackadder had it down to a science.
From my own family:"They don't have sense enough to pour piss out of a boot with the directions on the heel."
Oh! I just remembered these two from my family:1) This one is for when someone smart does something dumb/you overthink something until it becomes dumb: “so smart they eat their own mocos (snot)” and 2) when a rich person does something dumb: “all dollars and no cents (sense)”
I would also like to add: (Both, I believe said by Denver Pyle)
The Good Lord poured your brains, He used a teaspoon.
When the Good Lord was handing out brains, someone jostled his hand.
I don't remember where I heard this, but, "You couldn't find a clue in a field full of clues!"
If you got any denser, you'd make lead look light.
My favorites would be:"Hey. Look at it from the bright side. You made the hillbillys look smarter than they are."or"If you were smarter, you would be a real challenge for the toddlers here."
"You must've gotten into the gene pool when the lifeguard wasn't looking."
Well, you tried.
Where did you say you went to school?
Do you smell smoke?
I would challenge you to a battle of wits, but I see you are unarmed.
Never heard this one before it's good
HAHAH!Good job! Saved.
This is one of my favorites so far.
OMG That's rude and I love it.
This is very creative! Did you write it?
Awwww I'll save this one for future emergencies.
Nice, this is useful indeed