dumb as a rock
dumb as nails
stupidish
dumbish
dym
pratty
stupidass
dopey
thick as a whale omelette
dumb
dumb as a post
thick as mince
shit-for-brains
dumb as a stump
dumber than a rock
dumb as dirt
retarded
rock-dumb
bee-brained
thick as pig shit
numbskulled
dumber than a box of rocks
dumb as a doorknob
simpleminded
dumb like a fox
thick as a plank
dumb as a box of rocks
dumbassed
thick as two short planks
opaque
baka
muddlebrained
dunderheaded
numbnut
bull
one brick short of a full load
dumbbutt
thick
retardical
dumbass
dumb as an ox
thickheaded
asinine
dumb as a bag of hammers
fatuous
inane
bubbleheaded
tomfool
lamebrained
pillocky