Derogatory slang for a woman with an unattractive face; often used in a dismissive or insulting way. The term is dated and may be considered offensive.
不細工 is a general term for unattractiveness, applicable to both men and women, and is less slangy than おかちめんこ.
Etymology
The origin is uncertain. It may be a compound of おかち (a low-ranking servant or attendant) and めんこ (a dialectal or slang term for face), suggesting a face like that of a lowly servant. The kanji 御徒面子 are likely ateji.
