Dutch uncle
Paul Pry
Polonius
TV-viewer
admonisher
adviser
backseat driver
beholder
bird-watcher
busybody
butt-in
buttinsky
bystander
confidant
consultant
counsel
counselor
drugstore cowboy
expert
eyewitness
gaper
gazer
gazer-on
girl-watcher
goggler
guide
instructor
intermeddler
looker
looker-on
meddler
mentor
monitor
nestor
observer
ogler
onlooker
orienter
perceiver
percipient
pragmatist
preceptist
prier
pry
quidnunc
rubberneck
seer
sidewalk superintendent
snoop
snooper