電車内で無意識にオナニーしちゃうことありません？　だめだよ。

Have you ever masturbated on the train without thinking about it? You shouldn't.

The term Onabare(オナバレ) is a combination of the Japanese word for masturbation(オナニ) and a theorised old word for "To hide". The term refers to cases where someone is masturbating stealthily, sometimes when someone else in in the same room, sometimes while somewhat secluded.