Sand - I've seen birds do this. For me, it doesn't work. First - where can you get enough sand for a full-sized dude to bathe himself in? Only one answer to that question: the beach. But once you're there, your swimsuit covers many of the areas of most concern, hindering your ability to really get your cleanse on. Also: residue problems. Much scratchier and more troublesome than the "soap residue" seen in Dove commercials, using their special residue-revealing lighting.
Tongue - a cat specialty! But again, for me, problematic. It's impossible for me to really do more than my shins, feet, and parts of my arms. My hands are covered, but that's not really the problem. When I think "bathe" I'm thinking: cleanse the body whole. Any time it's just my hands that need washing, it's probably not something I want to lick off. I suppose one could say: get someone else to do it! They can reach all those areas easy. But that's a borderline-uncomfortable proposition to me. I'm one of those neurotics who, if someone wanted to give me a tongue bath, I'd want to be squeaky clean already before they started! I know, kind of dumb. But even if I were so inclined, still the tongue is not ideal. Cat tongues are practically designed to the purpose! (no theological debates please) They are raspy. The taste buds themselves seem sharp, hooked, and directional. Like some kind of pink, stretchy & extensible brush/comb system! The human tongue is not nearly so well-suited to the purpose. Nor is the human mouth-esophageal setup ready for the inevitable hairballs. This technique is a bad fit for non-felines.
Towel - towel-bathing. I guess they do this for infants. Presumably the towel is damp and warm. Sounds cute and adorable! I don't know much about it, though. I couldn't speak to the ways it could possibly be adapted for big people. I only just learned about this one while exhaustively researching this post. I had to include it for that reason alone.
Bathtub - plenty of people have gone on and on about this one. "The water just sits there! Gross. You're steeping in your own dissolved filth." But I say: I love a good tubber. I heart a nice long tub-soak. Ahhhh. I'll play three albums through, read half a book and when I'm done: ALL WARM AND WRINKLY! But I admit, when I pop the drain and the water runs out, I always stand up and follow it up with a shower. For me the tub is for relaxation, not cleansing.
Shower - way too involved to get into here. This deserves its own post.