One woman, outraged by the image, brought it to people's attention, and some of the first batch of responses were from men telling her it wasn't that big a deal and to get over it. That bothered me much more than the image itself, which I honestly think is okay. I'd be more likely to sport the "cold dead fingers" sticker myself, though.
One discussion list participant brought up a interesting point, asking if folks are more offended by the design or by the demographic to which the design is meant to appeal. (She didn't use the word "redneck," but that's more or less what she was getting at.)
For more on why the campaign and why some do view it as sexist, read the COSWL blog post and others' comments.