Most of the hook for online role playing games lies in the games themselves. Still, some games pander to prurient interests and provide significant pornographic content. Online games are not submitted to standard ESRB ratings, so they aren’t necessarily immediately identifiable by a rating (such as M for “Mature” players). Research and caution is advised as you explore the world of online game playing.
In addition to sexual content that is part of the game, many online games and virtual worlds permit, or even encourage, user generated content. As an example, Second Life is a virtual world—not really a game per se, since there are no objectives or imposed goals. The point of Second Life is creativity and users are encouraged to build and create their own worlds. That includes clothing (or lack thereof) for their avatars, as well as programmable behaviors that aren’t automatically part of the game. It doesn’t take a degree in rocket science to figure out where that’s going to go. And in virtual worlds like Second Life, there is plenty of that sort of content.