Counterpart stupidly bit me on purpose (8,6)
I believe the answer is:
opposite number
'counterpart' is the definition.
(synonyms)
'stupidly bit me on purpose' is the wordplay.
'stupidly' is an anagram indicator (a stupid ordering of the letters).
'bit'+'me'+'on'+'purpose'='bitmeonpurpose'
'bitmeonpurpose' anagrammed gives 'OPPOSITE NUMBER'.
(Other definitions for opposite number that I've seen before include "Counterpart" , "Direct competitor" , "One of similar status" , "pal!" , "colleague elsewhere" .)