Rusty Trombone

From Wikipedia: Rusty trombone is a sexual act in which a man stands with his knees and back slightly bent, with feet at least shoulder width apart to expose his anus. The other partner typically kneels behind the man and performs anilingus while reaching up beneath the testicles or around the body to manually administer rapid up and down motions of the penis, mimicking the motions of a trombone player. The act is defined primarily by the physical orientation of the partners and the combination of analingus with manual sexual stimulation; however, other positions and variations are possible.