There are innumerable stereotypes that can be based on race, gender, socioeconomic standing, level of intelligence, culture, political affiliations, religion, physical appearance, physical well-being, etc.
It cannot think of individual stereotypes that affect everyone. So much of stereotypical perceptions can be significantly biased based upon the culture in which we live. In America, a stereotype for men might be that they are supposed to be the leader of the family: the "bread winner." In our modern culture, women are not stereotypically expected to be homemakers, as in the past. However, women may be perceived to be weaker or perhaps not as intelligent (as opposed to men) based on some stereotypes.
There are stereotypes regarding white by blacks and vice versa. There are stereotypes regarding Democrats by Republicans and vice versa. People descended from one race may make assumptions about people from other races. Whites might be suspicious of other ethnicities. Christians may well harbor stereotypical beliefs about non-Christian faiths. After 9-11, many stereotypes exist regarding Muslims and the Islamic faith. People draw stereotypes about short men and blonde women. Teens are affected by stereotypes by older generations. For a long time, people with tattoos not the result of being in the Armed Forces or victims of the Holocaust were seen to have a lower social standing—though this is drastically changing with the renewed interest in "body art." Even people suffering from physical infirmities are treated differently, as they they are not intelligent because their body is unwell.
Stereotypes are a source of prejudice, and prejudice is not based upon fact, but ignorance. It is impossible to prove that stereotypes are credible because they are not based in fact. Some stereotypes are directed not to put people down, but to establish unfounded expectations of people. Christians are not supposed to sin. Teachers are not supposed to have typos on a paper. Lawyers are expected to be honest, as well as policemen.
The difficulty with stereotypes are that they are not true, but people treat others based upon these untruths. The Equal Employment Opportunity Act was designed to...
...ensure fair treatment to all segments of society without regard to race, religion, color, national origin, or sex.
This law was necessary to protect individuals who were not hired or paid fairly based on race, religion, color, gender, etc. These kinds of difficulties arose from stereotypes. However, the perception was not the only thing that was damaging: people were not getting paid commensurate with their education and experience because they were victims of a stereotype.
Another difficulty created is a stereotype threat: when someone of a group that is associated to a negative stereotype ends up (even without knowing it) fulfilling the stereotype.
For example: black people have the "less intelligent" stereotype attached to them, so a black person might perform poorly on an IQ test.
This might also apply to athletes and young women (particularly of school age). Stereotypes are sometimes a self-fulfilling prophecy when individuals "buy into" these negative beliefs.
Arrests made of suspected criminals based on their skin color and proximity to a crime is also tied to discrimination. Plenty of blue collar crime is committed by whites, and white collar crime is many times committed by whites.
Stereotypes prohibit equality to all under the law.