"A boring day" in English is commonly expressed as "a dull day" or "a tedious day". These expressions come from the adjectives "dull", meaning "lacking interest or excitement", and "tedious", meaning "boring or tiresome".

For example:

"Today was a dull day; nothing interesting happened."

"I spent the whole day doing paperwork, and it was extremely tedious."

中文翻译：

"今天是一个枯燥无味的一天，什么都没有发生。"

"我把整天都花在了文书工作上，真是极其乏味。"