After some coworkers invited me to a marathon of a certain series, I'm thinking a Zero costume could be potentially one of the most awesome costumes ever. Better yet, it would be difficult to tell who's in the costume.
The funny thing about this is that I thought of it while I was at work this morning, and just afterwards, the guy who sits next to me in my Japanese class said, "Hey, you know what would be the most awesome costume...?" Of course, he knew about the marathon, so it wasn't that big of a coincidence.
A few necessary components: actual fabric (too much plastic looks dumb), ruffled shirt, and not-cheap-plastic helmet.