"A dog's day" is a slang expression used to describe a day that has gone badly or turned out to be very unpleasant. It is often used in a negative context to describe a difficult or frustrating day. The origin of this expression is not clear.
Example:
It was a real dog's day at work today. Nothing went right.
It's been a dog's day and I just want to go home and relax.
Translation:
今天工作真是狗屎一天。什么都不对劲。
今天真是狗屎一天，我只想回家休息。