Horror Means Responsibility
As we start to embrace horror as a roleplaying genre, we also start to teeter on the edge of our own personal fears, and lines we do not wish to cross. This brings up the subject of two meta-gaming tools that are very important to the game: the Social Contract and the X Card. Many of you are already familiar with these tools, so we will just go over them briefly here.
First the Social Contract should be established, such that all the players realize they will be playing in a horror game and agree to play in the genre. The game system should be chosen thoughtfully, because different games approach horror in different ways, and that decision is also part of the Social Contract. The S.C. should inform the players of the overall length of the game, because a one-shot plays out with a different tempo than a campaign. Lastly, the players should establish the limits of exploration; for example, they may agree to have no child abuse or rape scenes of any kind.
A strong Social Contract can catch most of the major incidents that might arise, but it can sometimes miss things, and sometimes events at the table can get out of control faster than the contract can be invoked.
To help with this we have the X Card: a physical card you (or anyone) can raise or tap at any time, signaling to everyone playing that the current topic/event makes you uncomfortable. When the X Card is used, the table should quickly move beyond the issue without questioning the card's usage. I find that it's best to quickly fade the scene to black, or simply “yada yada” it.
Horror games are about exploring and confronting fear. Therefore before you enter into such a game, you should be aware of your own limits. It's during the creation of the Social Contract that the limits of your game should be determined, in order to minimize the use of X Cards during play.
If you find yourself facing a situation in which the other players want to explore your triggers, it's probably best to bow out of that game. If you're a considerate player you won't indulge in this sort of behavior; be mature about these issues, so everyone can enjoy the game to the greatest degree possible, within parameters you've all agreed upon.