My dad would say Cant see thru muddy water.. when we would sit in front of the tv

Slicker than snot on glass door knob

not the sharpest tool in the tool shed

Life is like a box of chocolates never know what your gonna get!!

One brick shy of a full load.

His elevator don't go all the way to the top.

Your brain is like a pea rattling around in a box car.

I see said the blind man to his deaf wife that is clear as mud.

Got his nose stuck so far up in the air he drowns when it rains.

Like John Wayne toilet paper, tougher than a cob and don't take carp off nobody.

Katy bar the door.

Dumber than a box of rocks

Porch lights on, ain't nobody home

My dad had quite an assortment.
some of the more memorable ones were:
when some major mess was involved - Scattered out like a wild women's chit in the moonlight.
when us kids were making a lot of racket - Come through here bellering like a bull ape in mating season.

From one of my first real job bosses who was a degreed engineer from A & M, worked at the Ford plant on Grand Ave,
and had won an award and a free car for coming up with the XLT truck package idea. But he grew up on a farm in Mexia and never forgot his roots or a sense of humor...

For something that smelled really ripe - That would run a bulldog off a tub of guts.
Similar but for different occasions - stronger than stud horse pizz with the foam farted off.
For a smashed finger - throbbing like a mocking birds azz in July.
for various things that were stuck like bolts and such - tighter than a bull's azz in fly time.
many more too numerous to list.

Colder than a well diggers a@@hole

Spit on those new shoes.
Shackeing like a dog S'ng peach seed.
Srcemming like a man on the wrong train.

Your brain is so small, if I laid it on a sharp edge of a razor blade it would look like a bb on a four lane high way.

Smoke them if you have them.

It�s gonna come a turd floater

Or "Sniffing farts out of seatcovers!"

Does the tin man have a sheet metal C*** ?

Sweating like a whore in church.

He�s so dumb he couldn�t pour p*** out of a boot with instructions on the bottom.

He couldn�t play dead in a western.

I could put these on here all day

The problem is that I don't even think about them until they fall out of my mouth.

Speaking from experience, don't say "Like a cow staring at a new fence" in front of foreigners unless you really want some funny looks.