If it is done in a private manner then it is difficult for moderators to put a stop to it. According to the official rules for the game, "NSFW/sexual/& or sexually suggestive behavior is forbidden. This applies to anyone manipulating the character animations/emotes to resemble mating/sex of any sort. This also includes custom mods such as animations, items, textures, sounds, music, etc. (Penalty: ban)." That is straight from Sura, so if you are having issues, just as Mac said, take a screenshot and send it off to a moderator.