Let me try it this way.

1. A: 有一种人（是），（无论）谁都看不上（他/她）。

       No one feels like giving a glance at him or her. (Maybe because he or she is homely, not physically attractive)

    B：另一种人（是），（无论）谁（他/她）都看不上。

       He or she is probably much too picky. There is hardly anyone he/ she would like to cast an cold eye on.

2. A: 有一种人，（他/她）不知道 什么叫做   爱。

       He/She has no sense of what love indeed is.

    B: 另一种人，（他/她）不知道什么叫    做爱。

       He/ She has no clue on how to make love/ have sex.

3. A: 原先，（这个人曾经）喜欢（过）一个人。---He or she once fell in love with someone deeply ( but this relationship didn't last for long or never worked out. That would be the reason why she or he lost their hopes towards a relationship.)

    B: 后来，（这个人）喜欢一个人（过）。----That is to say, he or she is now getting used to living alone without company. 这种人已经习惯自己孤独生活了。

Hope this would help~