numbnut
thick
retardical
bull
dumbbutt
dumb as an ox
one brick short of a full load
numbskulled
dumbassed
simpleminded
blockheadish
bodoh
stupidy
dopey
opaque
baka
nertz
dumbish
stupidass
dumbass
dunderheaded
thick as mince
sill
dumb as a doorknob
thick as a plank
dumb as a box of rocks
dumber than a box of rocks
goofball
thick as two short planks
pratty
lamebrained
muddlebrained
dumb as nails
shit-for-brains
dumb as a stump
retarded
dumb as dirt
dumb
thick as pig shit
dumb as a post
rock-dumb
dumber than a rock
thick as a whale omelette
bubbleheaded