Today’s idiom: get up on the wrong side of the bed
Meaning: when someone’s in a bad mood
Origin: Surprisingly it seems that there’s agreement on the origin of this phrase. Ancient Roman was superstitious about the left side; if one were to get out of the left side of the bed, or put their left foot down first, it would mean bad things. This superstition or mistrust of the left side has affected modern times as well, not just creating the above phrase. Not too long ago children in the US were not allowed to use their left hand for writing, cutting, etc. and were forced to use their right hand instead.