dysrationalia
rocks in one's head
not the sharpest tool in the shed
not the sharpest knife in the drawer
not the sharpest tool in the box
stupid
weak
unintelligent
simple
simpleton
acognitive
gormless
incompetent
vacancy
feeblemindedness
sophomania
light-witted
insensitive
dimwit
dickheadedness
noncognition
simplicity
childish
subintellectual
acataleptic
subnormality
underbrained
subnormal
unintelligence
incognizability
whifty
imperception
simple-minded
unskillfulness
blinded
nonintelligence
disorderly
simple-mindedly
indiscernible
folly
imbecility
not with it
unperceivingness
inconsideration
anoetic
mindblindness
inapproachability
stupidass
incompossibility
feeble-minded