agitator
anarch
anarchist
belittler
bellyacher
brawler
captious critic
carper
caviler
censor
censurer
common scold
complainant
complainer
crab
crank
critic
criticizer
croaker
extremist
faultfinder
griper
grouch
grouser
growler
grumbler
insubordinate
insurgent
insurrectionary
insurrectionist
insurrecto
kicker
kvetch
malcontent
maverick
momus
murmurer
mutineer
mutterer
nitpicker
nonconformist
pettifogger
querulous person
quibbler
reactionary
reactionist
rebel
revolter
revolutionary
revolutionist