Maybe we're the only one's in the world who think this, but sometimes watching a guy play with himself while fully-clothed is so much better than watching a guy who's plain ol' naked.
There's something about the way that a halfway pulled up wife beater squeezes a man's chest and the way an unzipped pair of jeans frames his dick that's incredibly sexy. Hell, if flexibility weren't so very important to us, we'd probably have sex fully-clothed all the time.