Why doesn't my friend wanting me watching A Game of Thrones?

My friend said that him and his family are watching a tv show called, "A Game of Thrones". I told him that it sounded good and I would try watching it But he freaked out and said, "No Marina. Don't watch it. I don't want you seeing the things in this tv show." He wouldn't tell me what was in it. He wouldn't tell me anything about it. It looks good and I want to know why he would tell me not to watch it! Help!