Nothing tells people you know a Mac inside and out like wearing a hat. Maybe it prevents the knowledge from escaping through your hair follicles, trapping it so it can be re-absorbed through your scalp.
Don't believe me? Click on the image below to go view Apple's video introduction to their workshops. I counted at least 6 hats the first time. And it's clear that baseball caps are not the best choice. I only saw one of those. It's probably because of the big hole in the back above where you adjust the size. But if you must wear a baseball cap, be sure it is fitted to prevent information leakage.