dead from the neck up
dumb as nails
opaque
tardish
peabrained
baka
dumb like a fox
dumb as a rock
dopey
shit-for-brains
dumb as a post
dumb
dumber than a rock
thick as pig shit
dumb as dirt
hammer-headed
rock-dumb
dumb as a stump
thick as a whale omelette
retarded
retardation
fuckwittedness
dym
bee-brained
stuuupid
frontal lobeless
shtus
muddlebrained
nuffy
fucktarded
daft
fatuitous
stupidass
boobery
dumber than a box of rocks
fatuous
thick as a plank
pratty
dumb as a box of rocks
asinine
dumb as a doorknob
thick as two short planks
inane
dumbass
dottle
thick as a brick
thick as mince
dunderheaded
dumbfuckery
stupidicy