Soda fountain hogs.
I don't drink soda very often at all, but when I do, I prefer the fountain drink over can/bottle.
There are those people out there that will somehow take up the whole space so you can't even begin to put ice in your cup, let alone hit the button to pour your soda. Its like you know someone is behind you, your soda is the last one out of the 8 fountains..MOVE TO THE SIDE. That same person then usually will drink some out of the cup before refilling it back to the top, all while still standing there.
Now of course, with the Freestyle machines Coke has, its not so much of an issue because its only one spout with 1,128 possible combinations.