I think it is a good idea for people to label their stories according to the gender(s) involved in the sexual activity. For example if a guy is trying to tell a story about him masturbating using his moms panties then he should say "M, Jerking to Moms panties" It depends on the people who are involved in the sexual activity. I think that is the toughest line to draw, for instance if I were jacking-off being watched by my girlfriend I would still label it M, because my GF isn't involved in Sexual activity she is just watching. However if it were me and my gf masturbating together it will be MF. If it is an all male group then just say all males. This way people would know what to expect and whether they are in the mood for your story or not. It would make the search a lot easier, for example if someone really enjoys reading about one guy masturbating then he can just look under M and start reading.
How about that?