Well, consider a mamas boy who spends most of his time with his mother and has few male role models. His mother might have a particular idea of what is proper behavior, which includes a lot of what is considered feminine. For example, she may teach him to always be polite in a very genteel way, like using very soft language and avoiding any form of roughness. He may also be influenced by the movies or books his mother likes, which might have a lot of feminine - centered stories. This continuous exposure to a feminine - dominated environment can lead to his femimization. He might start to show less interest in typically male - dominated activities like sports and more in things like cooking or sewing, which are often associated with femininity.
One example could be a mamas boy who is always dressed up neatly by his mother in a rather effeminate style from a young age. His mother might choose clothes for him that are more delicate or have softer colors, which gradually influences his appearance and gives an impression of femininization. Another instance could be a mamas boy who is so used to following his mother's advice on everything, including how to behave in a more 'gentle' way, which is often associated with femininity in some traditional views. For example, he is taught to be more passive and less assertive in certain situations.