1) That other nations worship false gods, instead of realizing that there is only one God of all nations, and that the other nations also worshipped that one God, albeit through different names.
That God told the Israelites to slaughter innocent people: men, women, children, infants, animals.
That only Christians can go to heaven.
2) My college roommate would only talk to me if she felt that in the conversation she could try to convert me. She prayed for me on the phone with her mother right in front of me, knowing I could hear every word. She thought I was going to hell, and she would openly pray about this in front of me. But she wouldn't talk to me, or invite me anywhere, unless she felt that by so doing, she could have a chance to convert me. I felt very dehumanized. I felt she thought I was so unworthy. And what irritated me so bad is she acted all perfect. But she had many sins that she hid, but I knew about them. Why couldn't she just admit her problems to me? I wanted to help her (she was bulimic) but she considered me unworthy to help her, since I was not a Christian.
3) I see exclusivism as dangerous. It is intolerant and leads to disrespect of other human beings who follow different ways.