My feeling on day time costumes is "Yeah right! Its F-ing hot out here!"
For that reason I try to stick to a wide brimmed hat and cotton clothes. Sadly, as a ginger kid, going with out a shirt will most likely mean I'll be dressed as a lobster by the end of the day.
As for night time guy clothes, my theory is "More Pockets! And More LIGHTS!"
The most important thing is to be comfortable! If you're not comfortable then you wont have as much fun.
And guys, don't put on a skirt just cause "At Burning Man, all the 'cool' guys wear skirts" I've always found it interesting that in BRC being "out side the norm" is so cool that "being out side the norm" becomes the normal. And once again, you're back in the normal. If you want to wear a dress or skirt cause it sounds fun have at it, but don't do it just because its not normal.