The particle yo functions to assert information that is new or unrecognized by the listener. In this context, yo adds emphasis to the speaker's assertion. It serves to jog the listener's memory or insist upon the validity of the previous command. It transforms the sentence from a passive complaint ("I said it...") into an active insistence ("I told you, remember?").
In the landscape of Japanese adult media, titles are often metaphors or euphemisms for sexual acts. This one is refreshingly literal. It directly confronts the subject matter, demanding the audience think about what happens after a request is made, and when that request is ignored. gomu o tsukete to iimashita yo
