英语“上厕所”有很多种说法：

go to the bathroom

use the toilet

answer the call of nature/ nature's call“响应大自然的召唤”

非正式的，有调侃的意味，最好在熟人和朋友之间使用。

I had to get up in the middle of the night to answer the call of nature.我得大半夜起来去响应大自然的召唤（上厕所）。

He went to answer the call the nature.他去上厕所了。

A：Where are you going? 你干嘛去？

B：Nature's call.大自然在召唤。