Is there a way to make it so the chit-chat forum is an option to users? Basically what i'm saying is you could make a check box under profile-->options (or whatever it is) to show or not show the chit-chat forum. This could include removing the forum from your main forum page all together or just making it so new threads dont appear. Or maybe it's possible to also make it so new chit-chat stuff doesnt show on the portal page when this option is turned off (chit-chat off).
W/O any knowledge of how this site is made it still seems like a lot of work.
