Face it - ADHD or not we all get annoyed by things. He's probably a lot like you and that usually causes conflicts as we hate things about other people we hate in ourselves. It's our nature.
You should check out Cognitive Behavior therapy. You'd learn new ways to deal with things like your being annoyed by your son-in-law. It truly helps with or without your meds.
And try to ask yourself why is his behavior so annoying to you? It may surprise you when you get the answers.