Keeping things IC, Raa's got a point. There should be a law forbidding rape.
OOCly, I agree that it's not the best topic to RP with. It doesn't mean that it's against the rules, but what goes against them is not keeping it PG. This means you can't be too explicit on main and the players should be on the same page about it OOCly. If you don't wish to be part of a rape RP, state it OOCly through tell. That should be enough for the player to back off and if he/she doesn't, you can report them and file a petition. But do this only if you explicitly say you do not wish to be part of that RP and your wishes are not respected, not if someone is RPing it, is IC, and within proper PG boundaries.
This sort of RP requires maturity not all players have, despite their age. It requires that the players know what not to say and how to approach other players about it. Sadly, some people can't do this and it all turns into an IOC mess it's better to avoid simply by not doing this kind of topic. Personally, I don't like censorship and I believe any topic can be RPed as long as they are addressed responsively and respecting game policies.
If you have any doubts, talk to a GM instead of confronting other players.