What groups of people are hurt by stereotypes? Why is it wrong to have stereotypes about these people? What behaviour and language is discrimination? What behaviour and language is politically correct?

There are several groups of people, that are hurt by the stereotypes the most. People of others races, sexual orientations, disabled people, people with unusual appearance. Everyone is different so judge anyone according to his race, appearance or social group is completely wrong. Some people can insult others, kick them or just laugh at them just because of stereotypes and it's called discrimination. We should respect everyone, don't use offensive words so we will be politically correct.