I don't agree that you should say something about NOT caring about his life. You don't want to ruffle his feathers and get him mad, or else you may NOT get your guitar back! He may just decide never to be home or never answer the phone when it's you, etc., when you're trying to set up a time to come get it.

I wouldn't say anything about the quality of his life. Just talk about WHEN you can get your guitar back -- you can always "let him have it" after you have the guitar in your possession.