interjection
damn it!; darn it!; bring it on!
Colloquial interjection expressing frustration, defiance, or a fighting spirit. Can be used when something goes wrong or when psyching oneself up to face a challenge.
なにくそ、もう一度やってみよう。
Damn it, let's try again.
なにくそ、負けるもんか。
Bring it on, I'm not going to lose.
Compound of 何 (nani, 'what') and 糞 (kuso, 'excrement'), literally 'what shit'. The exact historical derivation is uncertain, but it became a fixed interjection expressing frustration or defiance.