The new leader stupidly larked about, which was annoying (7)
I believe the answer is:
rankled
'was annoying' is the definition.
I can't tell whether this definition defines the answer.
'the new leader stupidly larked about' is the wordplay.
'leader' says to take the initial letters.
'stupidly' is an anagram indicator.
'about' is an insertion indicator.
The initial letter of 'new' is 'n'.
'larked' is an anagram of 'rakled'.
'n' placed within 'rakled' is 'RANKLED'.
'which' acts as a link.
Can you help me to learn more?
(Other definitions for rankled that I've seen before include "Caused lasting resentment and bitterness" , "resented" , "caused constant annoyance" , "Festered" , "caused persistent annoyance" .)