Lack tact in work, punching dull pain in the neck (4,1,5)
I believe the answer is:
drop a brick
'lack tact' is the definition.
(to drop a brick is to say something tactless)
'work punching dull pain in the neck' is the wordplay.
'work' becomes 'op' (operation, work done in an operating theatre).
'punching' is an insertion indicator (inserted letters punch or puncture others).
'dull' becomes 'drab' (synonyms).
'pain in the neck' becomes 'rick' (rick can mean a strain or sprain).
'op' inserted into 'drab' is 'dropab'.
'dropab'+'rick'='DROP A BRICK'
'in' is the link.
(Other definitions for drop a brick that I've seen before include "put foot in it?" , "Make a tactless remark" .)