non-responder
nonresponder
nonreactor
nonconsenter
nonlistener
noncooperator
inactive
nonreplier
silent person
nonadherent
dummy
unpleasant person
disagreeable person
noncomplier
orphan
intolerator
reluctant dragon
refusant
noncommunicant
brick wall
balker
nonrespondent
noncompliant
unsympathizer
baulker
nonsympathizer
disregarder
lukewarmist
nonsharer
nontalker
armchair quarterback
negativist
gobshite
dissatisfier
nondisputant
pococurantist
decliner
nonchooser
refuser
bottler
eccentric
unthinker
indifferent
Buridan's ass
stonewaller
mute
nonaccepter
the lights are on but nobody's home
tubelight
reacter