unsolicited explainer; know-it-all who lectures others
Colloquial, mildly derogatory term for someone who eagerly explains or teaches things without being asked, often seen as annoying.
He quickly turns into an unsolicited explainer, so it's hard to ask him questions.
At the drinking party, the person next to me was a know-it-all lecturer and I had to listen to him talk the whole time.
Standard kanji spelling for this colloquial noun.
Kana-kanji mixed spelling sometimes seen in casual writing.
Compound of 教え (oshie, 'teaching') + 魔 (ma, 'demon' or 'fiend'), suggesting someone possessed by a demon-like urge to teach. The exact origin is uncertain, but it follows a pattern of colloquial -魔 compounds describing obsessive behavior.