In place of wishing someone ‘good luck’, Italians take part in a superstitious exchange in which the fortune-wisher says, In bocca al lupo, and the receiver responds, Crepi! This could be loosely translated as: “Good luck making it out of the wolf’s mouth alive.” “Thanks, hopefully the wolf bites it, not me!"
It’s considered bad luck to respond just by saying grazie–a flub that instantly marks you as a novice Italian speaker (or a fatally distracted one).
Towards the end of my pregnancy a shopkeeper wished me In bocca al lupone. The ever-effusive Italians love to change the scale and effect of words by adding modifiers to the ends. In this case, the -one made the proverbial wolf especially big and scary. I loved it; talk about appropriate.