Here are some shots on a theme that's always fun. I tried this six years ago, but I think my skills have improved since then. (The back shot didn't line up quite as nicely as the front, though).
Obviously, real X-rays don't quite work this way (to the chagrin of every little boy who's ever purchased a pair of "X-ray Specs"). They use a form of electromagnetic radiation (high energy light) that [mostly] passes through your body, revealing the outline of your skeleton. But what if we could design a special material that appears transparent only under specific viewing conditions? Like the polarizing filter in a pair of sunglasses. We could design clothes using this material, so that when you put the glasses on, you could see right through them!
Think of the boon this would be to voyeurs and exhibitionists! Obviously, people wouldn't be forced or tricked into wearing this material, but those who don't mind could opt in. It would be like a special little treat for perverts. All would appear normal under regular viewing conditions, and only those who are "in on the secret" would have any idea what's going on. Voyeurs and exhibitionists alike could get a thrill, right out in public, and it wouldn't disrupt anyone or violate anybody's consent!
I think this is a brilliant idea, and it would be such harmless fun to play with. I'm doubtful about the likelihood of this kind of thing even being possible, though. And if you could get it working, there are bound to be some unforeseen problems, like stepping under a fluorescent light of a particular wavelength, and finding that your clothes have unexpectedly been rendered transparent to all onlookers! Still, it's a great idea - worth keeping in mind as our technology advances.*
*After reading an insightful article in Wired magazine, I'm thinking that maybe this sort of thing will be more practical as Augmented Reality becomes more widespread. Technology is a fascinating thing, and the future rarely develops quite like anyone expects it to (as a host of now out-of-date science fiction literature can attest to).
Here's a behind-the-scenes shot of my setup - a window screen propped precariously on two chairs, with a couple of wooden practice swords for stabilization. Hey, you gotta work with what you have!