如何委婉的拒绝别人的请求

不好意思,我手头有一些事情要处理.

come up就是"发生"的意思(to happen)

I'm afraid something urgent has come up.

恐怕有紧急事情发生.

We'll let you know if any vacancies come up.

一有空缺,我们就会通知你.