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