微不足道 -------- not worth mentioning

例句：
A: I don't know how to thank you. I am really very grateftal to you for stopping to help me.
真不知道该怎么感谢你。谢谢你停下来帮我。
B: Oh, that's all right. It is not worth mentioning actually.
啊，没什么。真的微不足道。

同义词：
insignificant
negligible trifling
be knee-high to a grasshopper

注释：
be grateful to sb 感激某人