intellectually challenged
cerebrally challenged
half-witted
mentally challenged
drool bucket
fool
divvie
dunderhead
dumbass
loggerhead
hammerhead
dunce
fuckhead
bonehead
numskull
muttonhead
knucklehead
blockhead
lunkhead
shithead
lackbrain
unintelligence
doltish
blonde
hammer-headed
underwitted
not the sharpest tool in the box
not the sharpest tool in the shed
not the sharpest knife in the drawer
ungenius
monkey
stupidass
dipshidiot
midget-minded
dirtbrain
gormless
vacancy
fuckwitted
stun
smooth-brained
pinheadedness
half-brained
light-witted
idiot
duuumb
underbrained
unknowledgeable
subnormal
thickheaded
Boeotian