When you pick up a beverage or drink mistakingly thinking it is one substance/flavor and only after taking a swallow to realize that it is in fact something different. This may be caused by the container which may make it look a different color or by simply not being able to see into the beverage container (such as a sports bottle) misleading the drinker into realizing only after tasting it that a misbeveration has occured.
The worst version of this happening is when a cigarette butt appears in your mouth when you pick up a can of soda/beer etc. only to realize it was previously used as an ash tray.
A dark colored beverage in a dark plastic cup is expected to be grape kool-aid, but upon downing a swig you realize it was actually iced tea...a misbeveration has occured.