This would seem to indicate that so long as the story was properly rated and had the appropriate warnings attached, the occasional “f-bomb” would be acceptable. The essay goes on to compare graphic sexuality to movie ratings. How close would this apply to profanity, though? Many R-rated movies contain quite a bit of foul language.
Although profanity is allowed in "Professor" fictions, stories will be rejected if f-bombs (and s-bombs, and other vulgarities) are dropped constantly throughout the story.
NC-17 fictions will not be posted on MuggleNet Fan Fiction. NC-17 fictions characteristically include extremely graphic violence, large amounts of profanity, and graphic sexuality.