A 10-year-old boy cries easily, and his friends often say, "Stop acting like a girl! Boys don't cry!" The boy still feels like crying, but he learns to stop the feeling before it leads to tears that his friends would see. This is an example of

Gender socialization

Explanation:

Based on the information provided within the question it can be said that this scenario is a perfect example of the concept known as Gender socialization. This refers to the process where individuals are taught by everyone around them, how to behave in a social environment based on their assigned gender.   Which is what is happening in this situation by the boys friends telling him to "Stop acting like a girl!