When my busty wife and I, an adolescent, went to a mixed-gender hot spring to wash each other, we couldn't contain our arousal and ended up doing it in the bathtub.

巨乳すぎる奥さんが、思春期の僕と混浴温泉に入って洗いっこしてたら、お互いのムラムラが押えきれず、お風呂場でヤッちゃった