a stopped clock is right twice a day
bungler
stumbler
fuckup
fumbler
sad sack
bumbler
blunderer
botcher
butcher
even Homer nods
disclarity
feckless
inept
unreliability
inaccuracy
too clever by half
instability
inconsistentness
brittle
unequal
inaccurateness
rock
bungling
unclarity
flaky
incompactness
splutter
flaked
inconsistency
wet end
stultify
fallibility
bulletproof
bang to rights
play dumb
error-proneness
Jenga
unreliably
nonreliability
know-nothing
misunderstandable
on accident
banjax
impersistence
misinformant
incompetent
trick
dicey
ineptly
errant
hinky
duffer
debatable
fecklessly
erroneousness
hit-or-miss
overspecify
inconsistently
a little knowledge is a dangerous thing
disprovability
incompetency
inconsistent
disputable
dodgy
contain multitudes
mismanageable
false
unaccurateness
mischeck
uncompatibility
noise
dereliction
underrecord
broken reed
willful neglect
delinquency
unpredictability
imprecision
faultiness
incompetentness
faultable
nitpicker
misinterpretable
impreciseness
tired
captious
unpredictedness
uncritical
faultfinding
fallible
inequitably
unreliableness
vagary
palooka
hair-trigger