A sneer? I beg to differ (4)
I believe the answer is:
gibe
'a sneer?' is the definition.
(thesaurus)
'i beg to differ' is the wordplay.
'to differ' indicates anagramming the letters.
'i'+'beg'='ibeg'
'ibeg' is an anagram of 'GIBE'.
(Other definitions for gibe that I've seen before include "Mocking remark" , "Dig, or a barbed comment" , "Scoff (at) - taunt" , "Barb, dig" , "A jeering remark" .)