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