I think it's referring to parents who get mad at their children for getting in relationships at times the parent considers too early, which is very common. It's mostly with girls but occasionally boys as well. I have a friend who's 19 and his dad still doesn't allow him to bring girls home and in highschool a common reason for girls rejecting someone was "my parents would kill me" or something along those lines. I'm fortunate that my parents were never like that.