Buttmachine is a song by That 1 Guy. Some sort of musician/artist playing a self-made musical instrument. It's a wonderful little video. Well worth a watch. I guess, as a warning, there are butts. But they are all clothed. And some of them are his.
It's also worth checking out this video of him playing his instrument *snort* live to see whatall he does to make such noises.
And thanks to Ectoplasmosis for the linkstravaganza.