Genesis 34 discusses an incident with Jacob's daughter, Dinah. Dinah was "defiled" by Shechem, son of the prince of the country where Jacob was living. Shechem and his father were very gracious about the whole thing, offering to marry Dinah and give her as large a dowry as Jacob wanted. But Jacob's sons, following the family tradition of deception, told Shechem that they would accept if he and every other male in the city were circumcised. Shechem agreed, and when all his men were sore after the operation, Jacob's sons slaughtered them.
All this to say: when you decide to have your way with a girl, first make sure you know who her relatives are.