What should a young man do towards his father who is harsh and ill-mannered with others, and does not accept advice, and is the young man considered sinful if he avoids his father because of his behavior?

The father's right is great, and the harshness of his character does not negate his right. His obedience is obligatory upon you as long as you are able to accompany him and follow him, even if it involves hardship, as long as it does not cause you harm. Ibn Taymiyyah said: "It is obligatory upon a person to obey his parents in matters that are not disobedience [to Allah]... This applies to matters that benefit them and do not cause harm. If it is difficult for him, but does not harm him, then it is obligatory; otherwise, it is not."

Your words about your father and your description of his actions with these negative terms contradict what a child should be with his father: humility, reverence, and lowering the wing, as Allah Almighty said: ﴿So do not say to them, "uff," and do not repel them but speak to them a noble word.﴾ [Al-Isra: 23]. A noble word is the word of a sinful servant to a harsh, stern master, and that your soul with him should be in the utmost humility.

It is permissible to advise the father gently, while observing proper etiquette, for advising parents is not like advising others. Imam Ahmad said: "He [the son] commands his parents to do good and forbids them from evil... He teaches him without harshness or offense, and does not speak to him in a harsh tone, otherwise he leaves it [the advice]." Filial piety is one of the greatest causes of Allah's pleasure and entry into Paradise, for the Lord's pleasure is in the father's pleasure.