I'm reading a manga in which I've come across the following exchange (for context the second character, B, has just beaten up A in a fight):
A: おのれ きさまなんぞに...
B: いいや あたしなんぞに てめーは敗れるのさ!!
My understanding of なんぞに was always that it could be used similar to "Why", so the first comment it simply something along the lines of "Bastard, idiot, why...", but I've no idea how it then functions in the response from B.
なんぞ directly after a noun is a variation of なんて/なんか/など, used to make light of something and express a negative/derogatory feeling. It does not contain the meaning of why. なんぞ sounds old-fashioned and is typically heard in fictional old man's speech.
In this conversation, きさま is a derogatory word and なんぞ even strengthens it, so it's okay to translate きさまなんぞ as "a bastard like you". B repeated なんぞ to emphasize the irony that A was defeated by that "bastard." ("And you are defeated by that bastard!")
なんぞ meant why in archaic Japanese (see examples from a 古語辞典), but it's almost never used in that way in modern Japanese.
