[wnorris]

no... if a user is in a group which displays a given forum, there is no way to have them join a group to hide that forum. When calculating permissions, it combines all the groups the user is in, and if any of them have "yes" for a given item then it evaluates as "yes". The best approach would be to create a secondary group that can view this forum and have the user leave the group if they don't want to see that particular forum. In order to auto-join the user to that group when they register, you'd need to create a plugin that is hooked at account creation and take advantage of the user data manager to add the group (I think it supports groups anyway).