What were they talking about?

today i came into my friend's conversation late and they were talking about how this girl we know "ripped her liner" and then they mentioned "imagine having to tell your dad that?" i felt it was rude to ask about what they were talking about, since they were obviosly talking about something scandalous that happened to that girl due to their tone of voice. but can someone translate what those 2 phrases mean (the ones in quotations)?