You may not force any player into a roleplay scenario that involves sexual actions or actions that could be seen as highly disgusting, unless all players present agree to it OOC'ly.
Due to the fact that many players find roleplaying certain activities disturbing and/or disgusting, you are required to ask the person you wish to roleplay with (as well as any other players in the area) if they wish to participate in such activity. This includes all kinds of sexual roleplay (sex, rape, harassment, etc) as well as highly disturbing/disgusting roleplay in general (extreme tortures, animal violence, etc).
This rule does not forbid you to commit such actions completely though - if the other party refuses to participate in the roleplay then it is simply skipped and still happens ICly, but should be simplified to a simple /do message (for example "/do Anna Smith would be brutally raped by John Doe." or "/do John Doe's left leg would be cut off with a chainsaw."). You can contact an administrator if you're unsure of whether your planned action falls under this rule or not.
Pedophilia, necrophilia and incest behaviour however is not allowed at all.