...just like a woman

When we experience something (personally or vicariously through reading, watching TV, conversations, etc) and we get a feeling that the event can be grouped in our mind with other similar events (which is a natural tendency of our brains) and that grouping reveals a negative stereotype of a group of people, we have committed mental bias. That is not to say that what we have thought is not true, but what we have done is convert a statistic into a rule. Usually, this comes along with emotional activation within the brain, often negative.

Stereotypes are often based upon some statistical activity done inside the brain, which then get encoded as beliefs. Usually a single event is not enough to create a belief change. A person who has had several negative experiences with dogs and few positive ones will react differently to being bitten by a dog than would a dog breeder/enthusiast. Furthermore, a person taught to believe and think in a certain way will follow the worn-in pathways, right or wrong.

Everyone has latent biases. No exceptions. Trying to understand them is more important than pointing fingers at those whose latent biases leak out. Allowing people the opportunity to grow, to try to rise above their biases, to find good counter-examples, is the best way to deal with this problem. And any statistical data that is true and supports a bias should be dealt with in the real world. If a person calls an truly ugly baby ugly, fix the baby! Truth should trump political correctness, but overgeneralizations are wrong.