I am so glad you wrote. If we were talking, the first question I’d ask is when all this obnoxious behavior started? If this is recent behavior, it might indicate the onset of dementia. But if it dates back all 25 years, then I wonder how it is that he has never been in some kind of treatment to help him be a fully functioning adult. As it is, it seems that the only way he knows he “counts” is by being the best at being worst. He certainly can’t be ignored.
I do suggest that you and your mother insist on a session or two with your dad with a licensed family therapist. (Your father isn’t likely to truthfully share your account of his behavior if you send him to a counselor on his own.) If he won’t go, you and your mom should go anyway. You need and deserve some help. The therapist will be able to help you all figure out if your dad needs treatment or if the family could benefit from establishing some new ways of interacting with him so it isn’t so distressing for you and your mom — or both.
I wish you well.