Get up on the wrong side of the bed

The phrase "get up on the wrong side of the bed" is an idiom used to describe someone who wakes up in a bad mood or is easily irritated, seemingly right from the start of their day. It implies that the person may be feeling grumpy, agitated, or generally unhappy. It is not meant to be taken literally, as it refers to the idea that a person's mood can be influenced right from the moment they wake up, depending on which side of the bed they get out of.