A dirty job - Christopher Moore

Charlie Asher is a pretty normal guy. A little hapless, somewhat neurotic, more of a Beta than an Alpha Male. Charlie's been lucky, though. He owns a building in the heart of San Francisco, and runs a second-hand store with the help of a couple of loyal, if marginally insane, employees. He's married to a bright and pretty woman who actually loves him for his normality. And she, Rachel, is about to have their first child.
But normal service is about to be interrupted. As Charlie prepares to go home after the birth, he sees a strange man dressed in mint-green
at Rachel's hospital bedside - a man who claims that no one should be able to see him. But see him Charlie does, and from here on out, things get really weird. . . .
People start dropping dead around him, giant ravens perch on his building, and it seems that everywhere he goes, a dark presence whispers to him from under the streets. Strange names start appearing on his nightstand notepad, and before he knows it, those people end up dead, too. Yep, it seems that Charlie Asher has been recruited for a new job, an unpleasant but utterly necessary one: Death.

It's a dirty job. But hey, somebody's gotta do it.