This is the perfect crime. As long as you're wearing something you usually wouldn't, no Halloween party bouncer will have a thing on you. I'm not sure what the fuck it's supposed to be. And that causes a problem - because you have to have a title for your costume. You can't walk into a party and announce yourself as 'something or another', people are going to call your bluff and start yelling that you're not really wearing a costume.
Titles are essential.
But don't worry, the name doesn't have to be very good. I titled this costume 'Supreme Mega Monster', mainly because while there's no way I'm going to win any contests with this one, at least I can take salvage in the fact that my costume's name is by far the most awe-inspiring. Nudist colony protestor. See, there's a million ways to avoid the 'costume required' clause. You just gotta use your brain a little bit.