Faced with a waiter or a person behind a counter, there's no way I'd order glass of a lime-and-raspberry half-sugar half-diet cola, for a number of reasons: I'm not going to bother looking through a menu to see what's available; it's not explicitly on the menu, and I don't know how the system behind the counter works, or how much extra might be charged for such an odd order; I don't want to be "That Guy".

If I want something half-way between a macchiato and a cappuccino, but with the coffee poured on top of the milk, then I'd rather do that by pressing buttons on a machine, than ask a server who relays it to a coffee wallah who then looks quizzically at the instructions and asks the server for clarification who then passes the question on to me...