Is it permissible for a Muslim to say to his father, "May Allah not forgive you, and may Allah take revenge on you," and is it permissible for him to shun his father if he (the father) loves isolation?

It is not permissible to supplicate against a father, even if he is unjust. Rather, one should supplicate for his guidance and improvement of his condition. There is no objection to avoiding his company for isolation if this does not harm the father or fall short of his rights. The Muslim should strive to be patient and benevolent towards his father, for there is a great reward in that, as honoring one's parents is among the greatest acts of drawing closer to Allah.