Clothing is REQUIRED.
You should be wearing clothes. No nudes allowed! Long pants are recommended. If you insist on wearing shorts because it's 100 degrees in Detroit in July, you should wear knee pads.
(And, as long as you're going to be wearing a shirt, you might as well talk to the guy at your hackerspace who uses the screen printing machine and make some sweet team t-shirts.)
You may want to avoid loose flowing clothing that can easily get caught in moving parts or drags on the ground, because safety.