Sounds like your FIL might be in the early stages of Alzheimers. Early symptoms often include stuff like irrational anger, inappropriate comments, and other things. Most people think of the memory loss being the most obvious, but sometimes its other things.
I think your dh probably knows something is going on, but doesn't want to admit it. Probably true of the FIL as well. Reacting in anger makes it seem like the FIL understood that knife sharpening, dishwashing or whatever was okay, and that the job he was doing was helpful. It might be that he actually did not understand why doing those things were so important to him, and when confronted, lashed out rather than dealt with the real issues.
Getting old is hard on people. They see their independence slipping away, their friends passing away, their bodies breaking down and their minds wandering. Depression is very common, and is often expressed as anger.
Not to excuse your FIL, especially considering the inappropriate comments, and other things, but try to see his perspective. Moving in with you, after a heart attack, has changed his life in many ways. He is living with children for the first time since his were raised, living in someone else's home, not able to decide what is for dinner or what toothpaste to buy. He knows he is slipping, tries to help in ways that make sense to him, and gets reprimanded. Maybe finding him useful, easy tasks around the house will help you both. At his age, the tasks should probably be something considered "manly". Have him sort the mail, bundle up the recycling, sweep the patio, sort hardware in the garage (everyone has screws and nails sitting around in the wrong place), tighten the doorknobs, take down the screens, etc.
I think your dh probably knows something is going on, but doesn't want to admit it. Probably true of the FIL as well. Reacting in anger makes it seem like the FIL understood that knife sharpening, dishwashing or whatever was okay, and that the job he was doing was helpful. It might be that he actually did not understand why doing those things were so important to him, and when confronted, lashed out rather than dealt with the real issues.
Getting old is hard on people. They see their independence slipping away, their friends passing away, their bodies breaking down and their minds wandering. Depression is very common, and is often expressed as anger.
Not to excuse your FIL, especially considering the inappropriate comments, and other things, but try to see his perspective. Moving in with you, after a heart attack, has changed his life in many ways. He is living with children for the first time since his were raised, living in someone else's home, not able to decide what is for dinner or what toothpaste to buy. He knows he is slipping, tries to help in ways that make sense to him, and gets reprimanded. Maybe finding him useful, easy tasks around the house will help you both. At his age, the tasks should probably be something considered "manly". Have him sort the mail, bundle up the recycling, sweep the patio, sort hardware in the garage (everyone has screws and nails sitting around in the wrong place), tighten the doorknobs, take down the screens, etc.