Why do people do this ?

On the second to last day of school my cl watched a movie called "The boy in the stripped pajamas" It was a really sad movie and at the end I cried. My friend ame close but she didn't. l cried a little bit but I was laughing at myself because I was actually crying. But when other people came over and seen me crying they just started laughing. I stopped laughing and they just kept laughing. They went on and on and made fun of me the next day. Why did these people just keep laughing and make fun of me? Oh and these kids weren't watching the movie they were talking the whole time. And yes I am a girl!