Translation of "Disappointing" in Chinese

How disappointing!

那么失望！

You are a disappointing person!

你这种人差劲吗！

I am sorry for disappointing you.

对不起，是我辜负你了。

The speaker didn't know his subject, nor did he speak well; in short, he was disappointing.

演讲者不熟悉他的主题，说得又不好，总之，他很糟糕。