Parasites in hospital get young man very annoyed (7-2)
I believe the answer is:
hangers-on
'parasites' is the definition.
(hanger-on is a kind of parasite)
'in hospital get young man very annoyed' is the wordplay.
'in' is an insertion indicator.
'hospital' becomes 'H' (abbreviation for hospital on maps).
'get' is a charade indicator (letters next to each other).
'young man' becomes 'son' (male child).
'very annoyed' becomes 'anger' (I am not sure about this - if you are sure you should believe this answer much more).
'h'+'son'='hson'
'hson' enclosing 'anger' is 'HANGERS-ON'.
Can you help me to learn more?
(Other definitions for hangers-on that I've seen before include "Sycophantic followers - dependants" , "Sycophants, unwanted followers" , "Persistent (and annoying) companions" , "Minions" , "Sycophantic associates" .)