Traditionally, FoLCDom pretty much held such things as taboo. There was a large core of fans who felt that the Superman character was a family-friendly icon and as such should be portrayed strictly as PG. Nfic, back then, was also a source of contention and the subject of many a flame war.
Along with any theme or subject matter that was considered out there.
Things have lightened up considerably these days, but I don't think there's much appetite for hardcore profanity. I'm in agreement that's no bad thing, in the main.
As far as it being OOC, Lois, of course, is a bit of a potty mouth - according to Perry's account of her skiing accident
So anything up to PG13 probably suits her on the gfic side of the boards.
I think there may be some guidence on what's taboo in the FAQS for the mbs.
LabRat