Human being is a very intelligent creation of God on the earth.

None but man has the capacity to think, talk, and act accordingly.

Mustn't he know how to behave well and perform good manners?

Parents are bound to teach their kids how they should behave with family members, neighbors, friends, and teachers./Parents are bound to teach their kids about their behaviour with people who are family members neighbours, friends, teachers, etc.

Modesty, humbleness, kindness, and courtesy are essential traits, and a well-behaving person has these traits.

Despite behaving well in front, some people speak evil of people behind.

This is a bad manner. / This is a poor manner.