I've never been a fan of billboard-type costumes—"I'm a lame YouTube video" or "I'm an iPhone"—but this giant Etch-a-Sketch costume is excellent. And it actually works. No, it's not filled with aluminum powder (that could get dicey). It simplifies the setup to using a marker and glass, but the complicated rod and wires setup to make it draw blotchy boobs and penises exactly like the one you had as a kid (but bigger, and on this dude) makes it plenty props-worthy. Check it out in action in the video below.
So, uh, what would you draw on this guy? [Instructables]