One that can’t stand half-hearted party host (5)
I believe the answer is:
hater
'host' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'one that can't stand half-hearted party' is the wordplay.
'one' becomes 'ha' (I am not sure about this - if you are sure you should believe this answer much more).
'that can't stand' becomes 'hate' (I've seen this in another clue).
'half' indicates taking half.
'hearted' means to look at the middle letters.
The central letter of 'party' is 'r'.
'hate' with half the letters taken is 'te'.
'ha'+'te'+'r'='HATER'
Can you help me to learn more?
(Other definitions for hater that I've seen before include "Heart (anag.)" , "Antipathetic type" , "Unpleasant type" , "One who shows intense dislike" , "One disliking" .)