Nag's expression of annoyance about broken pen (7)
I believe the answer is:
henpeck
'nag's' is the definition.
(I've seen this before)
'expression of annoyance about broken pen' is the wordplay.
'expression of annoyance' becomes 'heck' (I am not sure about this - if you are sure you should believe this answer much more).
'about' is an insertion indicator.
'broken' indicates an anagram.
'pen' anagrammed gives 'npe'.
'heck' going around 'npe' is 'HENPECK'.
Can you help me to learn more?
(Other definitions for henpeck that I've seen before include "Harass (husband)" , "Nag as domestic fowl might" , "Nag a husband" , "(Of a woman) continually criticise (a husband)" , "Nag like domineering wife or farmyard fowl" .)