short bus
dim-bulb
lunky
one fry short of a Happy Meal
dunny
lead-footed
peabrain
Boeotian
thick as a brick
beefheaded
thickheaded
swear
heavy
dym
blunt-witted
loggerheaded
fuckheaded
lameoid
boofheaded
lamebrained
thickwitted
dumb as nails
muddlebrained
dottle
thick-skulled
dumb like a fox
frontal lobeless
tardy
autistic
wooden-headed
dilatory
sweer
slowsome
boobyish
clodpated
dull-minded
midget-minded
drowsy
poky
blonde
cerebrally challenged
plumbeous
goofy ahh
intellectually challenged
fatuitous
nonsmart
sleepy
dumb as a doornail
bovine
weak-minded