Why is it, exactly, that making an NSFW post in the Off-Topic Forum is bannable? It is the place for "everything else," after all. Perhaps you could have people mark their posts with an NSFW tag, and if it's not marked, you are banned. You cannot view these posts unless you sign in.
Thoughts?
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This site is provided by our gracious hosts and they have decreed that it is to be a fun, family-friendly environment that can also be accessed at work. There isn't a need for NSFW material here.