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