I heard a new one today

[krutch]

Dumber then a box of rocks.
Slick as gorilla snot
Stupid enough to be twins
Horny as an acre of three peckered billy goats

[3jaw]

"If I owned him I would trade him off for stale bottle of pi$$, pour out the pi$$, break the bottle, and call it a good deal."

"Busier than a three legged cat covering up $hit."

[frankie]

he would have to be bigger to be any dumber he's full right now.

[C - ROSS]

Dumber than dead dog sh_t.

Ross

[Rex]

Shakes worse than a dog s**tting razorblades.

I heard that as "Shaking like a dog passing a peach pit"

[Ernie]

I would challenge him to a battle of witts, but I won't fight an un-armed man.

ernie

[Ernie]

Layer to dirty old man accused of rape..."About all they can charge you with is assault with a dead weapon."

ernie

[smalltime]

"He has hit rock bottom, and continued to dig"

"He's so dense, light bends around him."

After listening to a badly told joke:
Well, There's five minutes of my life I'll never get back.

[huntinguy]

< "Slicker than snot on a glass doorknob." >

That was the one I grew up hearing from dad etc.
...Lew...

We couldn't afford glass doorknobs

[Arcane]

They call him Lump Lump because one lump of clay isn't dumb enough.