Judging others is part of human nature. Some people tend to judge others by the way they look or dress. Others judge people by the way they act or behave or by the way they treat others. Others judge people without even knowing them.
Personally, I think we should not judge or criticize others. Instead, we should try to be more understanding, tolerant and helpful in order to avoid hurting others.
However, we can form an opinion about somebody by the way he treats others who are close to them or the way they react when others are ill, in need or have a problem...