Monday-morning quarterback
knocker
anathematizer
slater
hypercritic
carper
niggler
antisceptic
rubbisher
maligner
critiquer
nitpicker
disillusionizer
disfavourer
roaster
jeerleader
affronter
criticaster
figure of fun
antidisestablishmentarianist
momist
negativist
mook
disrespecter
discreditor
stereotyper
brickbat
incredulously
fartknocker
loser
Debbie Downer
criticizingly
mistruster
fulminator
smartmouth
gainsayer
paralogist
misappropriator
misguider
miscegenist
misunderstander
pass-remarkable
misrepresenter
scorpion
condescender
one to talk
badgerer
antiskeptic
underpredictor
heckler