wake up on the wrong side of the bed

The phrase "wake up on the wrong side of the bed" is an idiomatic expression that means to start the day feeling irritable, grumpy, or in a bad mood for no apparent reason. It suggests that someone's mood or disposition at the beginning of the day is negative or unfavorable, as if they had a bad start to their morning. This phrase is often used humorously to explain a sudden change in someone's behavior or demeanor.