He looks outside and sees his newspaper on the porch with the headline "BULLETS TO HEAD NO LONGER LETHAL." Reading the article (his window is really close to the porch -- work with me here), he discovers that scientists have finally found a cure for bullets and distributed it during the night. This doesn't sound very plausible, but our hero has a tragic flaw: he has a getting-shot-in-the-head fetish. All his life he's fantasized about getting shot in the head; only the knowledge that he would immediately die has kept him from indulging himself. So although he knows, rationally, that this news story is almost certainly mistaken, the temptation is now too strong to resist. His dream has come true. Without thinking, he pulls out one of the many guns he keeps nearby for just such a situation and fires.
Watching through binoculars, his arch-enemy -- a guy he once cut off in traffic -- cackles. His revenge is complete.
A week later, he's found dead in a locked room with a puddle of water and a goat, but that's another story.