This occurs when two mere aquaintances leave a location, and one individual says "goodbye" entirely too early. In this situation, the relationship is not yet close enough to openly acknowledge the incredibly awkward position they have now been forced into while walking to their immediate destination. This usually occurs while walking to vehicles, or separate apartments/rooms.
Josh: Goodbye, Colton!
Colton: See ya later, Josh!
(after an excruciating 30 second silent side-by-side walk to the parking lot, both Josh and Colton reach their vehicles and part ways.)
Colton: (says to self) Wow, that was a Premature Goodbye if I've ever seen one.