NSFB

NSFB means Not Safe For the Brain. It refers to any fic that makes a negative amount of sense. Sometimes rendered Not Brainsafe or NBS. It is akin to NSFW, and they sometimes overlap.

All Legendary Badfic and a good deal of badfic is considered NSFB, therefore one must take extreme caution to avoid reading it (unless of course, you're a masochist).