unsmartness
uncleverness
uningenuousness
smartness
unneatness
feeblemindedness
nonrationality
vapidity
jejuneness
tameness
jejunity
unrelatability
vapidness
unsubstitutability
unnimbleness
unknowableness
nonsubstitutability
simple
simpleton
unnoticeableness
uselessness
inconvenience
inapprehensibility
unplainness
dullness
garishness
nondifferentiability
inapprehensiveness
unskillfulness
unthinkingness
unpracticality
unsensuousness
unobligingness
inappropriateness
unfitness
unimportance
unworthiness
not the sharpest knife in the drawer
cleverishness
not the sharpest tool in the shed
subnormality
not the sharpest tool in the box
non-understandability
subtlety
incuriosity
unsuggestiveness
unnegotiability
infeasibility
unsaintliness
nonsensity