1. be in a bad mood
looks like someone woke up on the wrong side of the bed this morning!
This expression implies that the person in question's unpleasantness or irritability is not a momentary thing; they've been that way since they got up that morning. Another way of putting it would be to say: 'he/she has been in a bad mood all day.' It also implies that the person's mood is not in keeping with their usual disposition. Therefore you would not use this expression in reference to somebody who is always in a bad mood or generally unpleasant. In a social situation, if you feel a friend is being unnecessarily harsh or ill-tempered, you can freely use this expression, but in a professional environment, saying it to someone in a position of authority could be insulting.