When you bid someone a premature farewell, creating an awkward moment where the conversation has been ended, but the two people are still together. When the actual moment to physically part ways is at hand, a weak/awkward second goodbye is sometimes given. Usually happens with someone that you kinda know, but not enough to start up a new conversation.
Example:
(Tom sees Mel at movie theater)
Tom: Hey Mel great movie, huh?
Mel: Yeah it was good
Tom: I know. Well... see you at work.
Mel: Bye.
*both begin to walk silently in the same direction, right next to each other. (because they unknowingly parked in the same area)*
Mel: ...bye?...
Tom: *pretends not to hear, jumps into car, leaves*
Mel(alone): that was an awkward Prema-bye!
Example 2:
Steve: I said goodbye to Meagan at the bus stop today.
Bill: Yeah? cool!
Steve: Yeah except I said goodbye a minute too early and we were both waiting for the same bus.
Bill: Ouch! wicked prema-bye!
Steve: i know...