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