It starts at his work. People begin having personal talks in the elevator, completely oblivious to him. His coworkers start acting like he's not around. Finally his girl friend leaves him and nobody seems to be aware of his existence. He's not invisible, just "ignored".
It all climaxes when he decides to take-out his asshole boss while wearing a clown suit. Nobody notices him walking into the building where he works, not even the security guard. But when he does the deed, he suddenly meets Philipe.
Philipe is the leader of a group of Ignored who have decided to band together to become "Terrorists for the Common Man". They don't know why they are being Ignored, just that they are. This gives them the ability to do just about anything they want. They start by trashing offices, but their exploits grow. Eventually Philipe is planning out terrorists attacks. Bob, the narrator of the novel, starts to wonder if Philipe is stark raving mad.
The Ignored is an excellent little novel about the dehumanization we all face. It takes many strange turns, but never loses the reader. A recommended read to make your depressing day even more depressing.