〜もん／〜んだもん mon / n da mon
〜もん／〜んだもん（mon / n da mon）means “because…! (casual, pouty excuse)”. A very casual, often childish or pouty 〜もの, used to give a reason while excusing or defending oneself. Formation: V（普通形）＋もん ／ Aい（普通形）＋もん ／ Aな＋んだもん ／ N＋な＋んだもん
because…! (casual, pouty excuse)
N2Formation
V（普通形）＋もん ／ Aい（普通形）＋もん ／ Aな＋んだもん ／ N＋な＋んだもん
Explanation
A very casual, often childish or pouty 〜もの, used to give a reason while excusing or defending oneself. Equivalent to から/もの but emotional and spoken, frequent among children and in coquettish speech. 〜んだもん adds explanatory のだ for extra justification.
Examples
Note
Very informal; sounds childish or feminine/coquettish, so avoid in formal or polite situations. Often paired with だって at the start of the sentence.
FAQ
〜もん／〜んだもん — what does it mean and how is it used?
because…! (casual, pouty excuse). A very casual, often childish or pouty 〜もの, used to give a reason while excusing or defending oneself. Equivalent to から/もの but emotional and spoken, frequent among children and in coquettish speech. 〜んだもん adds explanatory のだ for extra justification.
〜もん／〜んだもん — how do you form it?
V（普通形）＋もん ／ Aい（普通形）＋もん ／ Aな＋んだもん ／ N＋な＋んだもん
〜もん／〜んだもん — any usage notes?
Very informal; sounds childish or feminine/coquettish, so avoid in formal or polite situations. Often paired with だって at the start of the sentence.