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