Annoy wrong side, concealing entreaties (9)
I believe the answer is:
displease
'annoy' is the definition.
(thesaurus)
'wrong side concealing entreaties' is the wordplay.
'wrong' is an anagram indicator.
'concealing' indicates putting letters inside.
'entreaties' becomes 'pleas' (plea is a kind of entreaty).
'side' is an anagram of 'dise'.
'dise' enclosing 'pleas' is 'DISPLEASE'.
(Other definitions for displease that I've seen before include "Vex" , "Nettle" , "Anger" , "Aggravate" , "Upset" .)