I am currently wearing a pair of cargo shorts, and a worn and faded Phish tour shirt (Clifford Ball shirt). I wore sandles, but take them off when I get here. And, of course, my BSD hat. I also haven't shaved in about 3 weeks, so I am scruffy.
Personally, I believe that a hacker does the best work, at work, when they can be made to feel that they are working at home.
Cheers,
KM