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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It's fine as it is. The NSFW post should stay banable, simply because they are "Not Safe".