I will avoid idiots after half-hearted expressions of sorrow (7)
I believe the answer is:
laments
'expressions of sorrow' is the definition.
(a lament is a mournful cry)
'i will avoid idiots after half-hearted' is the wordplay.
'will avoid' is a deletion indicator.
'idiots' becomes 'nits' (nit can mean a stupid person).
'after' says to put letters next to each other.
'half hearted' becomes 'lame' (I am not sure about this - if you are sure you should believe this answer much more).
'nits' with 'i' taken away is 'nts'.
'nts' put after 'lame' is 'LAMENTS'.
Can you help me to learn more?
(Other definitions for laments that I've seen before include "Mourns" , "elegies" , "Bemoans" , "Sad songs" , "Feels regret" .)