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