This is what the iPhone was made for. INK: Tattoo Simulator will save your ass (literally) from desecration by a massive tattoo of an obscure Star Wars character, the name of the girl you just met in your freshman college biology class and want to spend the rest of your life with, a portrait of Newt Gingrich or whatever kooky longing for ink your drunk mind might come up with.
Just take a photo of the body area you’d like to see prettied up, and the app will superimpose the image (also shot by you, or fetched from the photo stash on your iPhone) onto said body area. It runs pretty darn slow even on the iPhone 4 when we briefly checked it out, but the effect seemed sort of cool at first glance.
Of course, you could also use it (far more effectively) for simply repositioning a tattoo when you’re sober, but that’s hardly as interesting.