thick as a brick
retard
short bus
thick-skulled
dim-bulb
dunny
dozy
dense
obtuse
slow
dim
dumb
dull
slow on the uptake
dead from the neck up
lunky
dullness
poky
obtuseness
wooden-headed
blockish
dumb as nails
barren
blonde
letterless
dumb as dirt
dumb as a stump
rock-dumb
cerebrally challenged
thick as pig shit
shit-for-brains
intellectually challenged
retarded
dottle
bee-brained
dumb as a post
thick as a whale omelette
dumber than a rock
duncery
thickwitted
hammer-headed
boofheaded
slow study
lead-footed
one fry short of a Happy Meal
stupidicy
retardation
fuckwittedness
blunt
stupefiedness
loggerheaded
midget-minded
blunt-witted
dumbfuckery
foppery
illiterally
dullery
illiterately
ungenius
backward
dunderheadedness
thickheadedness
numskullery
dumb as a doorknob
dumb as a box of rocks
indocible
dunderheadism
brain damage
beefheaded
illiterateness
thick as a plank
weak-minded
dull-minded
dipshittery
dumber than a box of rocks
dumb like a fox
boobery
stockishness
thick as two short planks
shitwit
fuckheaded
pathetics
subexpert
fuckwit
jerk
booger brain
chowderheaded
ill-informed
boobyish
pinheaded
unlearned
Benny
overslow
swear
worse