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