英文の意味について

A:You know, George said to me that I was good for nothing.
B:Did he? That's a terrible things to say to a sweet person like you. Don't take him seriously. He's mean to everyone.
I was good for nothingと、 That's a terrible things to say to a sweet person like youの意味が分かりません。
どなたか教えて頂けないでしょうか？