I just stick with my own Fluxbox theme and find my own wallpapers. If there's a theme with a nude or slightly nude female, why does it really matter that much? If you get fired for something like that and you don't work in a place where a lot of minors come by, then just sue the place and move on. Or you can just get fired and take it all like a cold rod in the ass when you get a colonoscopy. However, I don't like doing things that way.
Unless the images offend you personally or you work in a day care center, I really don't see what's wrong. I mean, it's not like it's two people having sex, right?
