I don't know how much you follow crazy loser internet memes, but what you described is literally the apparent motive. Sexless jobless "beta" male declares war on alpha males who get women, and the women who denied him.
We had one of those shootings around here in Western PA about 6 years ago by a nutcase fitting that description, though he wasn’t jobless. He actually had worked at the same place as a good friend of mine.
http://www.huffingtonpost.com/2009/08/04/bridgeville-gym-shooting-_n_251411.html