A double-dip cruise is the special Western itinerary that
DCL does to Costa Maya and Cozumel that has TWO stops at Castaway Cay (Disney's private island). Doube-dip is a term DISers started using as soon as these itineraries were announced (about two years back, I think). There is one every month May through December of this year.
Sometimes you will also see the term double-dipping applied to the restaurants. It's what folks may do if they have a Palo reservation (the adults only restaurant). They may go to their regular rotation to be with the kids or group while they eat, then go off to Palo for their own dinner. Hence, double-dipping into two restaurants.
10 WEEKS TILL MY DOUBLE DIP!