メンチを切る

Etymology
Phrase composed of +  +.

derivation. on its own generally means, as in ,. That does not fit this idiom, however.

One explanation is that is an alteration of, as found in the synonymous Kansai expression. In this, menta is an alteration of : →  →. The standard term is also used metaphorically to mean a glare, a stare; a scolding; compare 🇨🇬, to eye. In this case, the phrase could be parsed as: menta o kiru → “to boldly eyeball someone” → “to glare in challenge”.

Phonetically, however, there is no clear mechanism for to change into. A more likely phonetic origin might be. In this case, the phrase could be parsed as: menchi o kiru → “to cut / break someone else's honor” → “to glare in challenge”.

The derivation may be a combination of the above, where menta may have been influenced by mentsu to become menchi.

Verb

 * 1)  to stare or glare in challenge; by extension, to pick a fight