Dinflation is the phenomenon that occurs at a restaurant when the diners realize the check will likely be split evenly and over order, causing the final check to be inflated. The dinflation/over order is generally late in the meal and may be an extra bottle of wine, a digestif (e.g. port), or dessert that you wouldn't normally order.
This phenomenon is particularly prevalent in situations where a meal is spread out over many shared courses, where a bottle of wine is ordered & shared, when some of the party shows up late complicating things, or when patrons are not carrying cash and the polite thing to do is simply "split the check X ways" to save the waiter the headache.
The evening started out pretty reserved with just the three couples. But after a round of appetizers and two bottles of wine, folks realized the check was going to be complicated. Dinflation occurred when they set caution to the wind, ordered the most expensive cut of meat and someone even ordered a cigar.