To be in a bad mood, grouchy

"Good morning" "Yeah? What's so good about it?" "Well well, look at who got up on the wrong side of the bed this morning..."

"Buon giorno" "Ah sì? Cosa c'è di tanto buono?" "Guarda guarda chi si è alzato con la luna di traverso questa mattina..."

He's been jumpy all day. He must have got out of bed on the wrong side this morning

È tutto il giorno che è nervoso; si deve essere alzato col piede sbagliato questa mattina

In many ancient cultures, left was synonym of evil and right synonym of good. In ancient Rome, everything that was on the right was a sign of the gods' protections, while whatever was on the left was a sign of bad luck. That's why ancient Romans, who were very superstitious, when getting out of bed, didn't put their left foot on the floor first