aplandoner
one who "abandons plans" or otherwise cancels, rejects, or changes plans at the last minute, leaving others involved in the plans feeling lonely, bored, and rejected
Kyle: Did you ask John if he is going to the movies tonight?
Kara: Yes, but I know he won't go. He is an aplandoner.
Kara: Yes, but I know he won't go. He is an aplandoner.