1. Don’t be upset that Peggy got angry with you; she’ll cool off soon. She always has a short temper when she gets up on the wrong side of the bed.
2. I’m sorry I yelled at you. I must have gotten up on the wrong side of the bed.

Originally this phrase was “got up left foot forward” and dates back to the ancient Romans. In their time, the left side of anything was seen as sinister or unlucky, and Romans believed it was bad luck to put the left foot down first when getting out of bed. The idea that left is bad continued for centuries and eventually the word left was replaced with wrong