Hi,
If that subforum is more than just nudity then it would not of course need any general warning, however in that case I believe it strengthens my case that a thread such as the aforementioned with full frontal nudity
should carry the appropriate warning especially if it is in a forum which does not necessarily contain nudity as you have suggested.
It should actually be rather easy to define what level of imagery would require the title, the title itself is a perfect indication, anything that would not be considered prudent for viewing in a typical work enviroment in the US or UK (Europe of course is far more liberal about such things) should bear the title. I know on another forum I frequent that it does include many glamour type shots which indeed would be considered to foster a 'hostile work enviroment' or whatever the politically correct catchphrase is these days.
This isn't a matter of prude or taste or whatever, it's an easily drawn line which can save some uncomfortable experiences in the workplace or indeed at home, all it needs is the title and heck we all know it will drive more traffic to the thread anyway