Not a decal, but one accessory that I definitely HATE are those ball-sacks that guys hang from their diff or tow hitch. I'm not going to post a pic because I think it's that ridiculous - makes me want to carry a pair of scissors around and get rid of them whenever I see them. So redneck and vulgar IMHO, and that's coming from someone who grew up in rural NC and appreciates dirty jokes.
So I assume, the giant fiberglass Boner on my car's roof would send you into an absolute coma