Refusal to tuck into any bug (5)
I believe the answer is:
annoy
'bug' is the definition.
(thesaurus)
'refusal to tuck into any' is the wordplay.
'refusal' becomes 'no'.
'to tuck into' means one lot of letters goes inside another.
'no' placed into 'any' is 'ANNOY'.
(Other definitions for annoy that I've seen before include "Make slightly angry" , "eat" , "Upset" , "Bother, irritate" , "Anger" .)