thick as a plank
dumb as a doorknob
thick as two short planks
dumber than a box of rocks
dumb as a box of rocks
rock-dumb
dumb as a stump
dumber than a rock
dumb as dirt
dumb
dumb as a post
thick as a whale omelette
thick as pig shit
retarded
shit-for-brains
thick as mince
stupidass
dumb as a bag of hammers
bee-brained
dumb as nails
shitwit
fuckwit
booger brain
dumbassed
numbskulled
simpleminded
numbnut
bull
one brick short of a full load
dumbbutt
retardical
thick
dumb as an ox
stupidish
thickhead
dumb as a rock
pillocky
witless wonder
mongtard
dopey
dumb like a fox
bodoh
blockheadish
stupidy
hash
dumben
dumb cluck
boaby
dope
mushhead