Sneer? I beg to differ! (4)
I believe the answer is:
gibe
'sneer?' is the definition.
(thesaurus)
'i beg to differ' is the wordplay.
'to differ' is an anagram indicator.
'i'+'beg'='ibeg'
'ibeg' with letters rearranged gives 'GIBE'.
(Other definitions for gibe that I've seen before include "Barb, dig" , "Insult" , "Hurtful remark" , "Mocking remark" , "A jeering remark" .)