What term did thorstein veblen use to refer to the behavior of those at the top of the social hierarchy when they engage in such activities as jetting off to a remote destination for dinner?

The answer is: Conspicuous Consumption

Conspicuous consumption is the type of consumption that is not made to fulfill your basic needs to survive, it's made for sophistication or to increase your social status.  

Jetting off to a remote destination for dinner is definitely very inefficient if the sole purpose is only to absorb necessary nutrients to your body. Sophistication or social status would most likely become the factors in such dinner activity.