Are you Bob's manager? Because, this is his Bob's manager's job. Bob's manager's only job, or at least, their main job.

It sounds as if you've tried. If Bob is lucky, they'll have a good manager who has experience, skills, and resources to help Bob more than you can. Maybe it's training, or a class - many managers have a training budget. Maybe it's a shift in Bob's responsibilities. Maybe Bob is in over his head, and this isn't the right career path for him.

You're not ratting Bob out my talking to the person Bob reports to. Bob's manager needs to know about this, so they can manage the situation. Bob's performance impacts the whole team. It's negatively impacting your work/life. If Bob's manager is blindsided by something Bob does, it's going to go far worse for Bob than if they are aware there's an issue and can take steps to address it.

Maybe Bob has a terrible manager? Maybe you know the manager DGAF and will jettison Bob? That's a more difficult situation. You have to decide if you want to spend the rest of your and Bob's combined time at the company being Bob's crutch. You can stop being Bob's crutch and let Bob dig his hole, or you can say something and hope Bob's manager will at least try to help Bob, or you can keep on doing someone else's job for them. That's up to you. What your describe, though, isn't going to be solved by giving Bob a self-help book, and IMHO, you're going Bob's manager's job for them, as well as doing Bob's.

This comment is brought to you thorn-free, courtesy of my laziness today.