If a girl keeps talking about a certain part of her body?

One of our good friends, Mel, keeps talking about her rectum. Sometimes just toilet humor and other times to do with in that sort of way. Our friends wonder sometimes if she is just obsessed with it like if you say, was that report really difficult? And she would say, well not as difficult as shoving it sideways up your rectum! So whats with her? Is she secretly expressing a fantasy or just really immature and silly?