In boca al lupo

Literally translates to into the wolf's mouth but is used to express, Good luck.

Its origin is not clear though the common story of the founding of Rome, and how a she-wolf took Romulus and Remus into her mouth, is likely associated in the minds of many Italians. There is a form response of, "Crepi il lupo," meaning "Die wolf!", though many folks may simply acknowledge the good intent of the sarcastic idiom with, "Grazie."