I had jury duty two weeks ago, and, there were 2 guys who looked ready to go work construction as soon as they got outta there, and two kids dressed in the "emo" style. Rule of thumb is to dress nice, as, after all, you are dealing (potentially) with the law, and it is a serious matter. So, dress business-like; should you decide to wear a kilt, thats fine, but wear something nice with it. At the very least, you'll start some conversations in the jury pool while waiting to see if you're selected.