There are all kinds of stereotypes. Popular ones include vegans or vegetarians that look pale, underweight, undernourished, and unhealthy along with gay males who look feminine and gay females who look masculine.
When it comes to the negative vegan stereotype, very rarely is that actually accurate or legit. In fact, vegans and vegetarians generally tend to be much healthier compared to their meat-eating counterparts.
When it comes to gay people, there is no doubt that feminine gay males and masculine gay females exist, but who cares; after all that's just the way they are. However, it's important to keep in mind that these stereotypes are not always accurate, for example, you wouldn't be able to guess most peoples' sexual orientation just by looking at them, considering most gay males are masculine and most gay females are feminine.
So if stereotypes are often inaccurate and hurtful, why do we have them? Well, long ago, humans relied on stereotypes for survival. We would judge our surroundings and the people/animals who surround us and determine how a good person differs from a bad person which would keep us safe. We did the same thing with animals. Animals with large teeth were dangerous and animals with small teeth were benign (even though that's not always true, it helped keep us alive and out of danger.)
Today, we often use stereotypes to judge and bully people. According to research from C.N. McRae and others, stereotyping is a shortcut that enables us to confer order on our complex society. The problem is that stereotyping leads to prejudice. This in turn leads to discrimination. All stereotyping is really is a simplified and standardized conception about the characteristics or expected behaviors of an identifiable group. As a result, we develop generalized perceptions about people based upon such things as the color of their skin, style of dress, sex, and sexual orientation.