I have a T-shirt (from thinkgeek.com, but I don't think they sell them anymore) that says NSFW Co-workers strongly cautioned (like a movie rating). I only wear it to work (on Saturdays).
I've got a ton of geeky t-shirts, mostly from threadless. I don't have any pictures of them currently, but maybe I'll upload them later. I've got robot t-shirts (too many, actually), Hitchiker's Guide shirts, Harry Potter band shirts (since my sister is in an HP band she usually has some leftover t-shirt that's too large for her...), etc.
Actually, I'm also a knitting and crochet geek...do those count? Though I haven't made that many pieces that I'd actually wear because I've botched a lot of projects.
my geekiest shirt is one I have recently made for me and the boy. The pic isnt great but you get the idea. His is on a orange shirt (and Chris recently uploaded it to his flickr) (http://flickr.com/photos/lockergnome/2692053238/) and mine is on a pink t