Selfish hoarder of alcohol those people put out after party (3,2,3,6)
I believe the answer is:
dog in the manger
'selfish hoarder' is the definition.
(I've seen this before)
'alcohol those people put out after party' is the wordplay.
'alcohol' becomes 'gin' (gin is an alcoholic spirit).
'those people' becomes 'them' ('they' refers to a group of people).
'put out' becomes 'anger' ().
'after' means one lot of letters go next to another.
'party' becomes 'do' (do can informally mean a party).
'gin'+'them'+'anger'='ginthemanger'
'ginthemanger' put after 'do' is 'DOG-IN-THE-MANGER'.
'of' acts as a link.
(Other definitions for dog in the manger that I've seen before include "error in farmyard?" , "party-pooper?" , "One not letting others use what they themselves have no use for" , "Spoilsport" , "that could disrupt nativity play" .)