Regret troll post (14)
I believe the answer is:
disappointment
'regret' is the definition.
(thesaurus)
'troll post' is the wordplay.
'troll' becomes 'dis' (I can't justify this - if you can you should believe this answer much more).
'post' becomes 'appointment' (I've seen this before).
'dis'+'appointment'='DISAPPOINTMENT'
Can you help me to learn more?
(Other definitions for disappointment that I've seen before include "Frustration" , "Let-down" , "Setback" , "Frustrating thing" , "unhappiness" .)