Black people are loud in movie theaters. Oh-no he didn't just say that. Am I racist because I said that? Maybe it is a socio-economic factor how people behave in a public situation? Wouldn't that be stereotyping poor people?
Let's look at a more meaningful situation where stereotypes might come in to play. Say you are in a dark alley. To your right is a group of black males in their mid-twenties dressed like they just stepped out of a rap video. To the left is a group of conservatively dressed middle aged women. Which direction are you going? I feel confident that you chose your left. Maybe the group to your right actually did just step out of a rap video and you could of met a celebrity and had a story to tell your friends. Maybe the group of women just escaped from a mental institution and are looking for prey. You never know, but what you know already told you what the safer bet is.
Stereotypes in themselves are never wrong. Your mind creates them to make sense of the world. If you did not have built in stereotypes you would never know how to react when encountering new people. Making stereotypes does not make you a racist. It just makes you a human being using an important life skill.
The danger of stereotypes is when you refuse to let go of them. Nobody ever conforms to all of the stereotypes you have assigned to them. When you have no other information to go on then your best bet is to reference your stereotypes. But you also need to make the effort to learn about each individual. Every group of people has some really great people; just as every group has people that are absolute scum. When given the chance, take the time to really know everyone you meet. You will meet people of all different backgrounds that will make your world a much more interesting place. If you happen to talk to a black person, tell them to shut up when I'm watching a movie.